# acer

7 years, 232 days

These are Posts that have been published by acer

### Lyapunov fractals

February 03 2013 by Maple 16

11

2

The following (downsized) images of Lyapunov fractals were each generated in a few seconds, in Maple 16.

I may make an interface for this with embedded components, or submit it in some form on the Application Center. But I thought that I'd share this version here first.

I'm just re-using the techniques in the code behind an earlier Post on Mandelbrot and Julia fractals. But I've only used one simple coloring scheme here, so far. I'll probably try the so-called burning ship escape-time fractal next.

Here below is the contents of the worksheet attached at the end of this Post.

The procedures are defined in the Startup code region of this worksheet.

It should run in Maple 15 and 16, but may not work in earlier versions since it relies on a properly functioning Threads:-Task.

The procedure Lyapunov can be called as

Lyapunov(W, xa, xb, ya, yb, xresolution)

Lyapunov(W, xa, xb, ya, yb, xresolution, numterms=N)

where those parameters are,

- W, a Vector or list whose entries should be only 0 or 1

- xa, the leftmost x-point (a float, usually greater than 2.0)

- xb, the rightmost x-point (a float, usually less than or equal to 4.0)

- ya, the lowest y-point (a float, usually greater than 2.0)

- yb, the highest y-point (a float, usually less than or equal to 4.0)

- xresolution, the width in pixels of the returned image (Array)

- numterms=N, (optional) where positive integer N is the number of terms added for the approx. Lyapunov exponent

The speed of calculation depends on whether the Compiler  is functional and how many cores are detected. On a 4-core Intel i7 under Windows 7 the first example below had approximately the following performce in 64bit Maple 16.

 Compiled evalhf serial (1 core) 20 seconds 240 seconds parallel (4 cores) 5 seconds 60 seconds

 > with(ImageTools):
 > W:=[0,0,1,0,1]: res1:=CodeTools:-Usage( Lyapunov(W, 2.01, 4.0, 2.01, 4.0, 500) ):

memory used=46.36MiB, alloc change=65.73MiB, cpu time=33.87s, real time=5.17s

 > View(res1);
 > W:=[1,1,1,1,1,1,0,0,0,0,0,0]: res2:=CodeTools:-Usage( Lyapunov(W, 2.5, 3.4, 3.4, 4.0, 500) ):

memory used=30.94MiB, alloc change=0 bytes, cpu time=21.32s, real time=3.54s

 > View(res2);
 > W:=[1,0,1,0,1,1,0,1]: res3:=CodeTools:-Usage( Lyapunov(W, 2.1, 3.7, 3.1, 4.0, 500) ):

memory used=26.18MiB, alloc change=15.09MiB, cpu time=18.44s, real time=2.95s

 > View(res3);
 > W:=[0,1]: res4:=CodeTools:-Usage( Lyapunov(W, 2.01, 4.0, 2.01, 4.0, 500) ):

memory used=46.25MiB, alloc change=15.09MiB, cpu time=33.52s, real time=5.18s

 > View(res4);
 >

### Cornelius Lanczos

January 30 2013 by

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4

A set of three taped video interviews with famous physicist and mathematician Cornelius Lanczos (1893-1974) has been made available online by the University of Manchester.

### Wish List: 16 + 2

December 05 2012 by Maple

This is a wish list for the version of Maple after whatever immediate next version is being developed.

It's about three-quarters of a year since Maple 16 came out, and if Maple follows its recent history of annual releases then development of new features of the very next release after 16 would be quite well along, and possibly even nearing completion. But that could mean that this is a good time to discuss wish lists for the version after that -- the version two releases after 16.

### contour integration

September 26 2012 by Maple

There are two interesting threads about definite integration on the usenet group comp.soft-sys.math.maple posted in the past few days.

The first thread is more about the wrong result coming out of Maple's int command when computing via its MeijerG method. Motivating examples there include

int(cos(t)/(1+t^k), t=-infinity..infinity);      # for k=10,12,14,...

The poster demonstrates using residues to obtain a terse result.

In the second thread the poster examines the ideas that the solutions involving RootOfs (as returned by the ftoc method) may suffer from numerical difficulties during floating-point evaluation and are unnecessarily complicated when re-expressed in terms of more standard functions (ie. allvalues, then simplification...).

For those interested, an existing contour method exists within int. It is not very strong however. One can examine its source using commands such as,

showstat(int/definite/contour);

showstat(int/definite/contour/def1);


etc.

See also Methods of contour integration on wikipedia.

### longitude and latitude

September 21 2012 by Maple

5

3

Following on from the 3D plots of the Earth globes in comments to an earlier post, here's some hacky code to grab longtitude and latitude.

(nb. This code attempts to send the IP address of your primary DNS to www.geobytes.com so don't run it if you don't want that action.)

if kernelopts(platform)="windows" then
res:=ssystem("ipconfig /all"): res:=res[2];
StringTools:-Search("Primary Dns Suffix",res);
ans:=StringTools:-Split(res[%+36..%+70])[1];
else
ans:=ssystem("hostname -y"...

### images on surfaces

August 17 2012 by Maple

12

13

Let's see how we can display patterns, or even images, on 3D plot surfaces. Here's a simple example.

The underlying mechanism is the COLOR() component of a POLYGONS(), GRID(), or MESH() piece of a PLOT3D() data structure. (See here, here, and here for some older posts which relate to that.)

The data stored in the MESH() of a 3D plot structure can be a list-of-lists or, more efficient, an Array. The dimensions of that Array are m-by-n-by-3 where m and n are usually the size of the grid of points in the x-y plane (or of points in the two independent parameter spaces). In modern Maple quite a few kinds of 3D plots will produce a GRID() or a MESH() which represent the m-by-n independent data points that can be controlled with the usual grid=[m,n] option.

The plot,color help-page describes how colors may specified (for each x-y point pair to be plotted) using a procedure f(x,y). And that's fine for explicit plots, though there are some subtleties there. What is not documented on that help-page is the possibility of efficiently using an m-by-n-by-3 or an m*n-by-3 datatype=float[8], order=C_order Array of RGB values or am m*n float[8] Vector of hue values to specify the color data. And that's what I've been learning about, by experiment.

A (three-layer, RGB or HSV) color image used by the ImageTools package is also an m-by-n-by-3 Array. And all these Arrays under discussion have m*n*3 entries, and with either some or no manipulation they can be interchanged. I wrote earlier about converting ImageTools image structures to and from 2D density-plots. But there is also an easy way to get a 3D density-plot from an ImageTools image with a single command. That command is ImageTools:-Preview, and it even has a useful options to rescale. The rescaling is often necessary so that the dimensions of the COLOR() Array in the result match the dimensions of the grid in the MESH() Array.

For the first example, producing the banded torus above, we can get the color data directly from a densityplot, without reshaping/manipulating the color Array or using any ImageTools routines. The color data is stored in a m*n Vector of hue values.

But first a quick note: Some plots/plottools commands produce a MESH() with the data in a list-of-lists-of-lists, or a POLYGONS() call on a sequence of listlists (eg. torus in Maple 14). For convenience conversion of the data to a 3-dimensional Array may be done. It's handy to use op to see the contents of the PLOT3D() structure, but a possible catastrophe if a huge listlist gets printed in the Standard GUI.

restart:
with(ImageTools):with(plots):with(plottools):
N:=128:

d:=densityplot((x,y)->frem((x-2*y),1/2),0..1,0..1,
colorstyle=HUE,style=patchnogrid,grid=[N,N]):
#display(d);

c:=indets(d,specfunc(anything,COLOR))[1];

/     [ 1 .. 16384 Vector[column] ]\
|     [ Data Type: float[8]       ]|
c := COLOR|HUE, [ Storage: rectangular      ]|
\     [ Order: C_order            ]/

T:=display(torus([0,0,0],1,2,grid=[N,N]),
style=surface,scaling=constrained,axes=none,
glossiness=0.7,lightmodel=LIGHT3):
#op(T); # Only view the operands in full with Maple 16!

# The following commands both produce the banded torus.

#op(0,T)(MESH(op([1,1..-1],T),c),op([2..-1],T)); # alternate way, M16 only

subsop([1,1]=[op([1,1],T),c][],T);


Most of the examples in this post use the command op or indets extract or replace the various parts of of the strcutures. Perhaps in future there could be an easy mechanism to pass the COLOR() Array directly to the plotting commands, using their color optional parameter.

In the next example we'll use an image file that is bundled with Maple as example data, and we'll use it to cover a sphere. We won't downsize the image, so that it looks sharp and clear (but note that this may make your Standard GUI session act a bit sluggish). Because we're not scaling down the image we must specify a grid=[m,n] size in the plotting command that matches the dimensions of the image. We'll use ImageTools:-Preview as a convenient mechanism to produce both the color Array as well as a 3D densityplot so that we can view the original image. Note that the data portion of the sphere plot structure is an m-by-n-by-3 Array in a MESH() which matches the dimensions of the m-by-n-by-3 Array in the COLOR() portion of the result from ImageTools:-Preview.

restart:
with(ImageTools):with(plots):with(plottools):

p:=Preview(im):

op(1,p);

/                    [ 235 x 354 2-D  Array ]
|                    [ Data Type: float[8]  ]
GRID|0 .. 266, 0 .. 400, [ Storage: rectangular ],
\                    [ Order: C_order       ]

/     [ 235 x 354 x 3 3-D  Array ]\\
|     [ Data Type: float[8]      ]||
COLOR|RGB, [ Storage: rectangular     ]||
\     [ Order: C_order           ]//

q:=plot3d(1, x=0..2*Pi, y=0..Pi, coords=spherical, style=surface,
grid=[235,354]):

display(PLOT3D(MESH(op([1,1],q), op([1,4..-1],p)), op(2..-1,q)),
orientation=[-120,30,160]);


### subexpressionmenu and Clickable Math...

August 03 2012 by Maple 16

6

1

Apart from the online description of this new Maple 16 feature here, there is also the help-page for subexpressionmenu.

I don't know of a complete listing of its current functionality, but the key thing is that it acts in context. By that I mean that the choice of displayed actions depends on the kind of subexpression that one has selected with the mouse cursor.

Apart from arithmetic operations, rearrangements and some normalizations of equations, and plot previews, one of the more interesting pieces of functionality is the various trigonometric substitutions. Some of the formulaic trig substitutions provide functionality that has otherwise been previously (I think) needed in Maple.

In Maple 16 it is now much easier to do some trigonometric identity solving, step by step.

Here is an example executed in a worksheet. (This was produced by merely selecting subexpressions of the output at each step, and waiting briefly for the new Smart Popup menus to appear automatically. I did not right-click and use the traditional context-sensitive menus. I did not have to type in any of the red input lines below: the GUI inserts them as a convenience, for reproduction. This is not a screen-grab movie, however, and doesn't visbily show my mouse cursor selections. See the 2D Math version further below for an alternate look and feel.)

 > expr:=sin(3*a)=3*sin(a)-4*sin(a)^3:
 > expr;

 > # full angle reduction identity: sin(3*a)=-sin(a)^3+3*cos(a)^2*sin(a) -sin(a)^3+3*cos(a)^2*sin(a) = 3*sin(a)-4*sin(a)^3;

 > # subtract -sin(a)^3 from both sides (-sin(a)^3+3*cos(a)^2*sin(a) = 3*sin(a)-4*sin(a)^3) -~ (-sin(a)^3);

 > # divide both sides by 3 (3*cos(a)^2*sin(a) = 3*sin(a)-3*sin(a)^3) /~ (3);

 > # divide both sides by sin(a) (cos(a)^2*sin(a) = sin(a)-sin(a)^3) /~ (sin(a));

 > # normal 1/sin(a)*(sin(a)-sin(a)^3) cos(a)^2 = normal(1/sin(a)*(sin(a)-sin(a)^3));

 > # Pythagoras identity: cos(a)^2=1-sin(a)^2 1-sin(a)^2 = 1-sin(a)^2;

 >

The very first step above could also be done as a pair of simpler sin(x+y) reductions involving sin(2*a+a) and sin(a+a), depending on what one allows onself to use. There's room for improvement to this whole approach, but it looks like progress.

In a Document, rather than using 1D Maple notation in a Worksheet as above, the actions get documented in the more usual way, similar to context-menus, with annotated arrows between lines.

I am not quite sure what is the best way to try and get some of the trig handling in a more programmatic way, ie. by using the "names" of the various transformational formulas. But some experts here may discover such by examination of the code. Ie,

eval(SubexpressionMenu);



The above can leads to noticing the following (undocumented) difference, for example,

> trigsubs(sin(2*a));

1       2 tan(a)
[-sin(-2 a), 2 sin(a) cos(a), --------, -----------,
csc(2 a)            2
1 + tan(a)

-1/2 I (exp(2 I a) - exp(-2 I a)), 2 sin(a) cos(a), 2 sin(a) cos(a)]

> trigsubs(sin(2*a),annotate=true);

["odd function" = -sin(-2 a), "double angle" = 2 sin(a) cos(a),

1                       2 tan(a)
"reciprocal function" = --------, "Weierstrass" = -----------,
csc(2 a)                            2
1 + tan(a)

"Euler" = -1/2 I (exp(2 I a) - exp(-2 I a)),

"angle reduction" = 2 sin(a) cos(a),

"full angle reduction" = 2 sin(a) cos(a)]


And that could lead one to try constructions such as,

> map(rhs,indets(trigsubs(sin(a),annotate=true),
>                identical("double angle")=anything));

{2 sin(a/2) cos(a/2)}


Since the annotate=true option for trigsubs is not documented in Maple 16 there is more potential here for useful functionality.

### convert/identifier

July 05 2012 by Maple

1

3

Here is a hacked-up and short convert/identifier procedure.

The shortness of the procedure should is a hint that it's not super robust. But it can be handy, in some simple display situations.

If I had made into a single procedure (named G, or whatever) then I could have declared its first parameter as x::uneval and thus avoided the need for placing single-right (uneval) quotes around certain examples. But for fun I wanted it to be an extension of convert. And while I could code special-evaluation rules on my convert extension I suppose that there no point in doing so since convert itself doesn't have such rules.

For the first two examples below I also typed in the equivalent expressions in 2D Math input mode, and then used the right-click context-menu to convert to Atomic Identifier. Some simple items come out the same, while some other come out with a different underlying structure and display.

 > restart:
 > convert/identifier:=proc(x)    cat(#,convert(convert(:-Typesetting:-Typeset(x),global),name)); end proc:
 > convert( 'sqrt(4)', identifier);

 > eval(value(%)); lprint(%);

#msqrt(mn("4"))

 >

 > lprint(%);

#msqrt(mn("4"))

 > convert( 'int(BesselJ(0,Pi*sqrt(t)),t)', identifier);

 > eval(value(%)); #lprint(%);

 >

 > #lprint(%);
 > convert( Vector[row](['Zeta(0.5)', a.b.c, 'limit(sin(x)/x,x=0)', q*s*t]), identifier);

 > eval(value(%)); #lprint(%);

As it stands this hack may be useful in a pinch for demos and purely visual effect, but unless it's robustified then it won't allow you to programmatically generate atomic names which match and inter-operate computationally with those from the context-menu conversion. Identifiers (names) with similar typeset appearance still have to match exactly if they are to be properly compared, added, subtracted with each other.

Extra points for commenting that the round-brackets (eg. in function-application) are displayed as black while the rest is in blue by default, if you have a workaround.  That also happens when using the usual context-menu driven convert-to-atomic-identifier of the Standard GUI.

Extra points for noticing that function names like sin are italicized and not in an upright font, if you have a workaround. How to discern which instances of fontstyle="normal" should be removed?

Points off for commenting that this whole hack doesn't provide anything new or extra for getting around automatic simplification.  :)

This is a one-liner hack. But maybe together we could turn it into something that closely matched what the context-menu generates.

### ImageTools and densityplot

June 23 2012 by Maple

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Many of us know that issuing plotting commands produces various kinds of plot data structure, the details of which are documented on the plot,structure help-page. That page covers most of the details, and a thorough read can reveal that the numeric data of a plot is often stored within such structures as either Array or Matrix.

But what about the result of a call to

### colour and 2D point-plots

June 19 2012 by Maple

5

4

Someone asked me the other week whether a color gradient could be easily applied to a high density point-plot, either vertically or horizontally graded.

Without thinking, I said, "Sure, easy." But when I got to a computer, and gave it a little thought, I realized that it's not that easy to do it efficiently. And it really ought to be, even for tens of thousands of points.

There is a help-page plot,color which briefly describes some things that can be done with coloring plots. As of Maple 16, it mentions a "color data structure" which can be created by calls to the new ColorTools package. There is an example on that page for a single color, but not for several colors concurrently. Using Colortools to get a list of colors, for many points, can be done. (And there ought to be such an example.) But for the case of many data points that uses quite a lot of memory, and is slow.

Also, there is no 2D plotting equivalent to the 3D plotting colorfunc functionality. There ought to be. And just as the 3D colorfunc should be fixed to take three arguments (x,y, & z) any new 2D colorfunc should be made to take two arguments (x & y).

So, how can we apply a color gradient on a 25000 2D-point-plot, shaded by y-value? One way is to notice that the various 2D and 3D plot data structures can now store an efficient m-by-3 (or m-by-n-by-3) C_order, float[8] Array for the purpose of representing the chosen colors. (That is not documented, but can be learned by observation and inspection of various example plot structures.) We know that such an Array is relatively memory-light, and can be produced very quickly.

What this task has become is a 2D version of this method of inserting a custom made color sequence into a 3D plot, but more efficient on account of using a float[8] Array.

To get some decent timings the attached worksheet uses the time[real] command. Timings are computed both immediately after computation (same execution block) as well as after plot rendering (next execution block).

It takes about 1 sec for the Maple 16.01 64bit Standard GUI on Windows 7 to throw up and render the plot, for both methods.

It takes 3.4 sec, and a 108 MB increase in allocated memory, to compute the plot data structure result using ColorTools and a list. But it takes only 0.45 sec, and a 20.5 MB increase in allocated memory, to compute an equivalent plot data structure using the float[8] Array. (Timings on an Intel i7-960.)

[worksheet upload is misbehaving. So inlining the code.]

restart:
N:=25000:

xy:=LinearAlgebra:-RandomMatrix(N,2,generator=0.0..1.0,
outputoptions=[datatype=float[8]]):

str:=time[real]():

plots:-pointplot(xy,
color=[seq(ColorTools:-Color([xy[i,2],0,0]),i=1..N)],
symbolsize=4);


time[real]()-str;

3.323

time[real]()-str; # in new execution group

4.400
kernelopts(bytesalloc);

107646976

restart:
N:=25000:

xy:=LinearAlgebra:-RandomMatrix(N,2,generator=0.0..1.0,
outputoptions=[datatype=float[8]]):

str:=time[real]():

p:=plots:-pointplot(xy,color=red,symbolsize=4):

c:=Array(1..N*3,(i)->if(irem(i,3)=1,xy[(i+2)/3,2],0),
datatype=float[8],order=C_order):

subsindets(p,specfunc(anything,COLOUR),z->'COLOUR'('RGB',c));


time[real]()-str;

0.483

time[real]()-str; # in new execution group

1.357
kernelopts(bytesalloc);

20545536


### Matrix/Array access: order can be import...

June 06 2012 by Maple

7

0

Way back in Maple 6, the rtable was introduced. You might be more familiar with its three types: Array, Matrix, and Vector. The name rtable is named after "rectangular table", since its entries can be stored contiguously in memory which is important in the case of "hardware" datatypes. This is a key aspect of the external-calling mechanism which allows Maple to use functions from the NAG and CLAPACK external libraries. In essence, the contiguous data portion of a hardware datatype rtable can be passed to a compiled C or Fortran function without any need for copying or preliminary conversion. In such cases, the data structure in Maple is storing its numeric data portion in a format which is also directly accessible within external functions.

You might have noticed that Matrices and Arrays with hardware datatypes (eg. float[8], integer[4], etc) also have an order. The two orders, Fortran_order and C_order, correspond to column-major and row-major storage respectively. The Wikipedia page row-major  explains it nicely.

There is even a help-page which illustrates that the method of accessing entries can affect performance. Since Fortran_order means that the individual entries in any column are contiguous in memory then code which accesses those entries in the same order in which they are stored in memory can perform better. This relates to the fact that computers cache data: blocks of nearby data can be moved from slower main memory (RAM) to very fast cache memory, often as a speculative process which often has very real benefits.

What I'd like to show here is that the relatively small performance improvement (due to matching the entry access to the storage order) when using evalhf can be a more significant improvement when using Maple's Compile command. For procedures which walk all entries of a hardware datatype Matrix or multidimensional Array, to apply a simple operation upon each value, the improvement can involve a significant part of the total computation time.

What makes this more interesting is that in Maple the default order of a float[8] Matrix is Fortran_order, while the default order of a float[8] Array used with the ImageTools package is C_order. It can sometimes pay off, to write your for-do loops appropriately.

If you are walking through all entries of a Fortran_order float[8] Matrix, then it can be beneficial to access entries primarily by walking down each column. By this I mean accessing entries M[i,j] by changing i in ther innermost loop and j in the outermost loop. This means walking the data entries, one at a time as they are stored. Here is a worksheet which illustrates a performance difference of about 30-50% in a Compiled procedure (the precise benefit can vary with platform, size, and what else your machine might be doing that interferes with caching).

Matrixorder.mw

If you are walking through all entries of an m-by-n-by-3 C_order float[8] Array (which is a common structure for a color "image" used by the ImageTools package) then it can be beneficial to access entries A[i,j,k] by changing k in the innermost loop and i in the outermost loop. This means walking the data entries, one at a time as they are stored. Here is a worksheet which illustrates a performance difference of about 30-50% in a Compiled procedure (the precise benefit can vary with platform, size, and what else your machine might be doing that interferes with caching).

Arrayorder.mw

### faster fractals

May 22 2012 by Maple

12

8

Using techniques previously used for generating color images of logistic maps and complex argument, attached is a first draft of a new Mandelbrot set fractal image applet.

A key motive behind this is the need for a faster fractal generator than is currently available on the Application Center as the older Fractal Fun! and Mandelbrot Mania with Maple entries. Those older apps warn against being run with too high a resolution for the final image, as it would take too long. In fact, even at a modest size such as 800x800 the plain black and white images can take up to 40 seconds to generate on a fast Intel i7 machine when running those older applications.

The attached worksheet can produce the basic 800x800 black and white image in approximately 0.5 seconds on the same machine. I used 64bit Maple 15.01 on Windows 7 for the timings. The attached implementration uses the Maple Compiler to attain that speed, but should fall back to Maple's quick evalhf mode in the case that the Compiler is not properly configured or enabled.

The other main difference is that this new version is more interactive: using sliders and other Components. It also inlines the image directly (using a Label), instead of as a (slow and resource intensive) density plot.

Run the Code Edit region, to begin. Make sure your GUI window is shown large enough for you to see the sides of the GUI Table conveniently.

The update image appearing in the worksheet is stored in a file, the name of which is currently set to whatever the following evaluates to in your Maple,

cat(kernelopts('homedir'),"/mandelbrot.jpg"):


You can copy the current image file aside in your OS while experimenting with the applet, if you want to save it at any step. See the start of the Code Edit region, to change this filename setting.

Here's the attachment. Comments are welcome, as I'd like to make corrections before submitting to the Application Center. Some examples of images (reduced in size for inclusion here) created with the applet are below.

### Location marker for Plot Component

April 26 2012 by Maple

4

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The Locator object is a nice piece of Mathematica's Manipulate command's functionality. Perhaps Maple's Explore command could do something as good.

Here below is a roughly laid out example, as a Worksheet. Of course, this is not...

### repeating wrapper (DirectSearch)

April 25 2012 by Maple

6

3

Here is a short wrapper which automates repeated calls to the DirectSearch 2 curve-fitting routine. It offers both time and repetition (solver restart) limits.

The global optimization package DirectSearch 2 (see Application Center link, and here) has some very nice features. One aspect which I really like is that it can do curve-fitting: to fit an expression using tabular data. By this, I mean that it can find optimal values of parameters present in an expression (formula) such that the residual error between that formula and the tabular data is minimized.

Maple itself has commands from the CurveFitting and Statistics packages for data regression, such as NonlinearFit, etc. But those use local optimization solvers, and quite often for the nonlinear case one may need a global optimizer in order to produce a good fit. The nonlinear problem may have local extrema which are not even close to being globally optimal or provide a close fit.

Maplesoft offers the (commercially available) GlobalOptimization package as an add-on to Maple, but its solvers are not hooked into those mentioned curve-fitting commands. One has to set up the proper residual-based objective function onself in order to use this for curve-fitting, and some of the bells and whistles may be harder to do.

So this is why I really like the fact that the DirectSearch 2 package has its own exported commands to do curve-fitting, integrated with its global solvers.

But as the DirectSearch package's author mentions, the fitting routine may sometimes exit too early. Repeat starts of the solver, for the very same parameter ranges, can produce varying results due to randomization steps performed by the solver. This post is branched off from another thread which involved such a problematic example.

Global optimization is often a dark art. Sometimes one may wish to simply have the engine work for 24 hours, and produce whatever best result it can. That's the basic enhancement this wrapper offers.

Here is the wrapper, and a few illustrative calls to it on the mentioned curve-fitting example that show informative  progress status messages, etc. I've tried to make the wrapper pretty generic. It could be reused for other similar purposes.

Other improvements are possible, but might make it less generic. A target option is possible, where attainment of the target would cause an immediate stop. The wrapper could be made into an appliable module, and the running best result could be stored in a module local so that any error (and ensuing halt) would not wipe out the best result from potentially hours and hours worth of conputation.

restart:
randomize():

repeater:=proc(  funccall::uneval
, {maxtime::numeric:=60}
, {maxiter::posint:=10}
, {access::appliable:=proc(a) SFloat(a[1]); end proc}
, {initial::anything:=[infinity]}
)
local best, current, elapsed, i, starttime;
starttime:=time[real]();
elapsed:=time[real]()-starttime;
i:=1; best:=[infinity];
while elapsed<maxtime and i<=maxiter do
userinfo(2,repeater,iteration ,i);
try
timelimit(maxtime-elapsed,assign('current',eval(funccall)));
catch "time expired":
end try;
if is(access(current)<access(best)) then
best:=current;
userinfo(1,repeater,new best ,access(best));
end if;
i:=i+1;
elapsed:=time[real]()-starttime;
userinfo(2,repeater,elapsed time ,elapsed);
end do;
if best<>initial then
return best;
else
error "time limit exceeded during first attempt";
end if;
end proc:

X := Vector([seq(.1*j, j = 0 .. 16), 1.65], datatype = float):

Y := Vector([2.61, 2.62, 2.62, 2.62, 2.63, 2.63, 2.74, 2.98, 3.66,
5.04, 7.52, 10.74, 12.62, 10.17, 5, 2.64, 11.5, 35.4],
datatype = float):

F := a*cosh(b*x^c*sin(d*x^e));

/   c    /   e\\
F := a cosh\b x  sin\d x //

infolevel[repeater]:=2: # or 1, or not at all (ie. 0)
interface(warnlevel=0): # disabling warnings. disable if you want.

repeater(DirectSearch:-DataFit(F
, [a=0..10, b=-10..10, c=0..100, d=0..7, e=0..4]
, X, Y, x
, strategy=globalsearch
, evaluationlimit=30000
));
repeater: iteration  1
repeater: new best  9.81701944539358706
repeater: elapsed time  15.884
repeater: iteration  2
repeater: new best  2.30718902535293857
repeater: elapsed time  22.354
repeater: iteration  3
repeater: new best  0.627585701120743822e-4
repeater: elapsed time  30.777
repeater: iteration  4
repeater: elapsed time  47.959
repeater: iteration  5
repeater: new best  0.627585700905294148e-4
repeater: elapsed time  55.221
repeater: iteration  6
repeater: elapsed time  60.009
[0.0000627585700905294, [a = 2.61748237902808, b = 1.71949329097179,

c = 2.30924401405164, d = 1.50333106110324, e = 1.84597267458055], 4333]

# without userinfo messages printed
infolevel[repeater]:=0:
repeater(DirectSearch:-DataFit(F
, [a=0..10, b=-10..10, c=0..100, d=0..7, e=0..4]
, X, Y, x
, strategy=globalsearch
, evaluationlimit=30000
));

[0.0000627585701341043, [a = 2.61748226209478, b = 1.71949332125427,

c = 2.30924369227236, d = 1.50333090706676, e = 1.84597294290477], 6050]

# illustrating early timeout
infolevel[repeater]:=2:
repeater(DirectSearch:-DataFit(F
, [a=0..10, b=-10..10, c=0..100, d=0..7, e=0..4]
, X, Y, x
, strategy=globalsearch
, evaluationlimit=30000
),
maxtime=2);

repeater: iteration  1
repeater: elapsed time  2.002
Error, (in repeater) time limit exceeded during first attempt

# illustrating iteration limit cutoff
infolevel[repeater]:=2:
repeater(DirectSearch:-DataFit(F
, [a=0..10, b=-10..10, c=0..100, d=0..7, e=0..4]
, X, Y, x
, strategy=globalsearch
, evaluationlimit=30000
),
maxiter=1);

repeater: iteration  1
repeater: new best  5.68594272127419575
repeater: elapsed time  7.084
[5.68594272127420, [a = 3.51723075672918, b = -1.48456068506828,

c = 1.60544055207338, d = 6.99999999983179, e = 3.72070034285212], 2793]

# giving it a large total time limit, with reduced userinfo messages
infolevel[repeater]:=1:
Digits:=15:
repeater(DirectSearch:-DataFit(F
, [a=0..10, b=-10..10, c=0..100, d=0..7, e=0..4]
, X, Y, x
, strategy=globalsearch
, evaluationlimit=30000
),
maxtime=2000, maxiter=1000);

repeater: new best  3.10971990123465947
repeater: new best  0.627585701270853103e-4
repeater: new best  0.627585700896181428e-4
repeater: new best  0.627585700896051324e-4
repeater: new best  0.627585700895833535e-4
repeater: new best  0.627585700895607885e-4
[0.0000627585700895608, [a = 2.61748239185387, b = -1.71949328487160,

c = 2.30924398692221, d = 1.50333104262348, e = 1.84597270535142], 6502]


### animation of 3D plot rotation

January 24 2012 by Maple 15

8

6

Suppose that you wish to animate the whole view of a plot. By whole view, I mean that it includes the axes and is not just a rotation of a plotted object such as a surface.

One simple way to do this is to call plots:-animate (or plots:-display on a list of plots supplied in a list, with its insequence=true option). The option orientation would contain the parameter that governs the animation (or generates the sequence).

But that entails recreating the same plot each time. The plot data might not even change. The key thing that changes is the ORIENTATION() descriptor within each 3d plot object in the reulting data structure. So this is inefficient in two key ways, in the worst case scenario.

1) It may even compute the plot's numeric results, as many times as there are frames in the resulting animation.

2) It stores as many instances of the grid of computed numeric data as there are frames.

We'd like to do better, if possible, reducing down to a single computation of the data, and a single instance of storage of a grid of data.

To keep this understandable, I'll consider the simple case of plotting a single 3d surface. More complicated cases can be handled with revisions to the techniques.

Avoiding problem 1) can be done in more than one way. Instead of plotting an expression, a procedure could be plotted, where that procedure has option remember so that it automatically stores computed results an immediately returns precomputed stored result when the arguments (x and y values) have been used already.

Another way to avoid problem 1) is to generate the unrotated plot once, and then to use plottools:-rotate to generate the other grids without necessitating recomputation of the surface. But this rotates only objects in the plot, and does alter the view of the axes.

But both 1) and 2) can be solved together by simply re-using the grid of computed data from an initial plot3d call, and then constructing each frame's plot data structure component "manually". The only thing that has to change, in each, is the ORIENTATION(...) subobject.

At 300 frames, the difference in the following example (Intel i7, Windows 7 Pro 64bit, Maple 15.01) is a 10-fold speedup and a seven-fold reduction is memory allocation, for the creation of the animation structure. I'm not inlining all the plots into this post, as they all look the same.

restart:
P:=1+x+1*x^2-1*y+1*y^2+1*x*y:

st,ba:=time(),kernelopts(bytesalloc):

plots:-animate(plot3d,[P,x=-5..5,y=-5..5,orientation=[A,45,45],
axes=normal,labels=[x,y,z]],
A=0..360,frames=300);

time()-st,kernelopts(bytesalloc)-ba;

1.217, 25685408

restart:
P:=1+x+1*x^2-1*y+1*y^2+1*x*y:

st,ba:=time(),kernelopts(bytesalloc):

g:=plot3d(P,x=-5..5,y=-5..5,orientation=[-47,666,-47],
axes=normal,labels=[x,y,z]):

plots:-display([seq(PLOT3D(GRID(op([1,1..2],g),op([1,3],g)),
remove(type,[op(g)],
specfunc(anything,{GRID,ORIENTATION}))[],
ORIENTATION(A,45,45)),
A=0..360,360.0/300)],
insequence=true);

time()-st,kernelopts(bytesalloc)-ba;

0.125, 3538296


By creating the entire animation data structure manually, we can get a further factor of 3 improvement in speed and a further factor of 3 reduction in memory allocation.

restart:
P:=1+x+1*x^2-1*y+1*y^2+1*x*y:

st,ba:=time(),kernelopts(bytesalloc):

g:=plot3d(P,x=-5..5,y=-5..5,orientation=[-47,666,-47],
axes=normal,labels=[x,y,z]):

PLOT3D(ANIMATE(seq([GRID(op([1,1..2],g),op([1,3],g)),
remove(type,[op(g)],
specfunc(anything,{GRID,ORIENTATION}))[],
ORIENTATION(A,45,45)],
A=0..360,360.0/300)));

time()-st,kernelopts(bytesalloc)-ba;

0.046, 1179432


Unfortunately, control over the orientation is missing from Plot Components, otherwise such an "animation" could be programmed into a Button. That might be a nice functionality improvement, although it wouldn't be very nice unless accompanied by a way to export all a Plot Component's views to GIF (or mpeg!).

The above example produces animations each of 300 frames. Here's a 60-frame version:

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