MaplePrimes - answers and comments on Question, what is the Maple equivalent of Matlab's axis ([-inf inf -inf inf]) ?

example?

jakubi — Sat, 27 Jun 2009 04:00:11 Z

Do you have a specific example of the effect of that Matlab command?. In this page, I do not see something specific about:

axis ([-inf inf -inf inf])

but just the case of a single "inf".

automatic single limit

jakubi — Sat, 27 Jun 2009 05:13:03 Z

Yes, this automatic single limit case is clear to me. In fact, I have requested this functionality many years ago... And I think that I have even found some workaround.

But still I do not find clear the case of all four "inf".

min, max

jakubi — Sat, 27 Jun 2009 11:06:40 Z

Not sure yet about the case of the abscissa, for a function y(x) say, as normally either you choose the plot interval or let maple use its default (like -10..10)

For the ordinate, though, it is basically a matter of finding min and max for y(x) on that interval. One way to find ymin and ymax is using the lists [x,y] for the plot points in the 'plot' data structure:

p:=plot(cos(x), x=0..2*Pi):
L2:=map(x->op(2,x),op([1,1],p)):
ymax:=max(L2);
ymin:=min(L2); 

                              ymax := 1.

                    ymin := -0.999995190907583154

view

jakubi — Tue, 30 Jun 2009 20:14:03 Z

You mean something like this?:

mydisplay2 := proc(p,l)
    local xy, xmin, xmax, ymin, ymax:
    local L1, L2:
    xmin:=-10: xmax:=10:
    L1:=map(x->op(1,x),op([1,1],p)): xmax:=max(L1): xmin:=min(L1):
    L2:=map(x->op(2,x),op([1,1],p)): ymax:=max(L2): ymin:=min(L2):
    xy := (xmin,xmax,ymin,ymax)-> 
    plots:-display(plottools[line]([xmin,0],[xmax,0],thickness=3), 
    plottools[line]([0,ymin],[0,ymax],thickness=3), 
    view=[xmin..xmax,ymin..ymax]):
    plots:-display({p,xy(op(l))},
    view=[l[1]..l[2],l[3]..l[4]]):
    print(%):
end proc:

p := plot(cos(x), x=-2*Pi..2*Pi):
mydisplay2(p,[-2,2,-0.5,0.5]);

Draw gridlines over axes

pchin — Wed, 01 Jul 2009 19:10:49 Z

Patrick writes: "I want to plot two thick lines to be used to overwrite plot axes (a workaround for the inability to customize the axes)."

A workaround that doesn't require figuring out the y-axis range is to use custom gridlines. For example, try the following:

> plot(cos(x), x=xmin..xmax, axis=[gridlines=[[0], thickness=4], tickmarks=8], axes=normal);

This produces thick gridlines at x=0 and y=0 only. You have to add a tickmarks suboption because otherwise, Maple assumes that you want tickmarks at the same locations as gridlines by default.

Paulina Chin
Maplesoft

an example

PatrickT — Sat, 27 Jun 2009 04:35:07 Z

thanks jakubi,

this is a very good link to the Matlab function, actually.

Let me explain how the inf and -inf can be used. Consider the following:

> xmin:=-2*Pi: xmax:=2*Pi:
> plot(cos(x), x=xmin..xmax);

Maple automatically selects the maximum and minimum values along the y-axis. For this specific example, I can reproduce the look of the plot by doing the following (Maple13/classic):

> ymin:=-1.05: ymax:=1.05:
> plot(cos(x), x=xmin..xmax, view=[xmin..xmax,ymin..ymax]);

I was able to guess by trial and error that Maple selects something like -1.05 and 1.05 as the minimum and maximum values of the y-axis.

If I want to plot the positive quadrant only (for some reason), then I set the ymin and ymax as follows:


> ymin:=0: ymax:=1.05:

But while I *know* that I want to select ymin:=0, I can only *guess* that I need ymax:=1.05. And if I change some parameters of my function that "optimal" ymax value may change as a result (while my ymin will not)

with Matlab I would have obtained the desired result by setting:

> ymin:=0: ymax:=inf:

Matlab *knows* that the appropriate value of ymax is 1.05 in this case, and automatically selects another value if I change the parameters of my function.