## 284 Reputation

19 years, 18 days

Professor of Economics SUNY Stony Brook I use Maple for Research: To test theoretical modelling ideas with various kinds of general equilibrium deterministic and stochastic models in Macroeconomics and Urban Economics. Graduate classes: In Macroeconomics and Econometric classes. Undergraduate classes: In Urban Economics and Computational Methods classes. Note: You can communicate with me in German and French as well as English.

## Bug(?): Disappearing Input with View|Sho...

This week I made up an exam using Maple where I didn't want the input to be visible. I used View|Show/Hide to accomplish that. This worked alright within a short time frame. I could save the file with the input hidden, and then I could reload the file and, upon re-checking input to show, all the input would re-appear. However, when I let the file sit for a few days and then tried to re-show the input today, all the input in each execution group was condensed into one line with '?'.

This sure seems like a Maple bug to me. Does anyone have any other ideas about how this could happen? Or how one might recover the input?

## Working around a bug in plots[implicitpl...

Maple
When doing an implicit plot recently, I ended up with a whole large triangle which was completely tessellated with much smaller triangles. The checking of other graphs and numerical data of the function in this region, it was very clear that the implicit function should be a well defined line in this region. Further look at the code for implicitplot() indicated that, after some setup work, it ultimately called exactly the same routine (`plot/iplot2d`()) as plots[contourplot]() with the option "contours=[0]" to do the actual calculations. I then discovered that when I called contourplot() directly with the "contours=[0]" option I got a correct implicit curve consistent with my other data and with no tessellations.

## An easily corrected limitation to symbol...

Maple
As currently programmed, fsolve() does not do numerical derivatives for systems of equations. The reason for this is that subs() is used instead of eval() when evaluating derivatives. [Note: jacob is the symbolically defined jacobian of the system of equations and lsub is the sequence of appropriate numerical substitutions (not the "list" of substitutions the mnemonic might suggest).] The original statement (in `fsolve/sysnewton`) is: A:=traperror(evalf(subs(lsub,jacob),Digits-5+n)); The functions evalf() and subs() apparently do no know how to work together to produce numerical derivatives. However, the following statement does work.

## Dealing with Hidden Indention Characters...

Maple
Maple displays a defined procedure (yours or Maple's)as output when you enter definition or when you execute eval(). It should be noticed that in either case, Maple uses its own well defined indention scheme, regardless of what indention scheme you used or didn't use when you input the procedure. Now if you want to edit the procedure, and your only copy is gotten by copying Maple's output to an input line, you will have to deal with Maple's hidden indention characters at the beginning of each line. I have been unable to find any Help material on this, and, in particular, I have not been able to find any way to edit (delete or input) these characters directly. However, they are all invisibly located in the blank space, which is visible, at the start of each indented line. The code seems to be of the form "indent a fixed number of spaces more than the previous line". These fixed numbers are one of three values, a positive number (approx. 3), 0, or a negative number (approx. -3).

## Tips on dealing with Maple Standard's e...

Maple
As most of you have probably experienced, even Maple 10.4 in standard 2D Maple input has some strange editing behavior. Most of it is of the variety of "What you see is Not what you get". There are two basic kinds of things that can happen: (a)You get strange errors that seem impossible from the code that you can see, such as "missing operation" or "object used as name" or even "non-matching delimiters"; and (2) Your editing action happens much further away or much more extensively than your cursor position or highlighting would indicate. This apparently happens because Maple is creating a parsing structure on the fly behind what you are editing and not visible to you. When some incomprehensible errors happen or Maple seemingly does not want to allow you to edit what you see is wrong, sometimes the only remedy is to retype whole blocks of code (possibly creating other errors in the process requiring the same cure, etc., etc.). Till Maple can supply us with a structural viewer that would allow us to easily find and correct such problems, I want to pass along some tips I have learned in my frustration.
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