again, I wish Maple help can be better. A simple example of how to use listplot on matrix is all what is needed.

I have a matrix, 3 rows and 5 columns. I need to use listplot to generate 3 listplots on same graph. I can do this one row at a time. But when calling listplot(m) where m is the matrix, it gives error

Error, (in plots:-pointplot) incorrect number of coordinates in points data

Clicking on the above link, as usual sends me to page that says There is no help page available for this error

Help says

The listplot command also accepts a list or Matrix containing points data. great. But how?? I click on the link next to the above line, it sends me to page about pointplot. There is says that pointplot also accepts a matrix of size n by 2. Does this mean listplot matrix must also be two columns? It does not say this on the listplot help page.

For a workaround, I now generate plot of each row on its own, then use display to put them all on same graph. But the problem with this is that all have same color. I was hoping that if Maple did it all at once, it will automatically pick different color for each line as is the case with Mathematica (example below)

Is there a better way to do this? For reference, I'd like to generate similar plot like this

You see, the colors are automatically selected. With manual plotting of each row myself, I have to select the color myself and to make sure they are different and so on. It will be better if the system did all of this.

Please see attached worksheet

Download how_to_list_plot_matrix.mw

What is the correct way to use listplot with matrix?

I am not able to even trap this Maple exception.

Any suggestions what to do? It is not a problem if it can't solve it, but I need to at least be able to  trap the exception in order to go to the next one, else the whole program now stops when it hits this.

I used try..catch but this exception just ignores this and escapes to top level. This is not the first time I've seen Maple exception escape the try/catch. I do not understand why some do that and some not. I

Is this another bug?

Download how_to_trap.mw

Update 3 years later. FYI. This error still shows in Maple 2025. It will be nice if Maple returns no solution than an internal error that can not be trapped which means the whole program crashes.

Download internal_error_march_27_2025.mw

It will be great if  DEtools:-convertAlg  which is designed to find coefficients of a linear ode, not to expand the coefficients it finds.

This caused my patterns to fail, as after putting the coefficients in a certain form, and then calling DEtools:-convertAlg later on somewhere else in the program, the patterns no longer worked due to this unexpected expansion.

It will be better if DEtools:-convertAlg returns the coefficients it find as is and not expand them. I could not find an option to use for this. Here is an example.

restart;
ode:=b*(x+x^2)*diff(y(x),x$2)+x*(2*a - 1)*diff(y(x),x)+c*y(x)=0;

After the call the coefficients become

L:=DEtools:-convertAlg(ode,y(x))

You might ask that one can easily "fix" this afterwords. Sure. I can use collect on x. But the point is that in general, it might not be clear what to collect on or what the changes that were made are.

In principle, it is better to keep the coefficients in same form as they were in the ode so that the ode do not change form.

Maple 2022.1 on windows.

I have an expression and I want to select the part of the expression which has diff(y(x),x) in the expression.

Using select(has,expr,diff(y(x),x) works, except when the expression happend to be exactly diff(y(x),x) in this case select returns diff()

I understand why this happens. But I can not avoid this problem by say first checking if the expression has more than one operand, because nops(diff(y(x),x) is 2 and not one. Also 1+diff(y(x),x) has two operands. And I can not check if the expression is of type `+` or `*` before, because other types can have more than one operand also.

So now what I do is the folliwng: first check if the expression has diff(y(x),x). If so, convert the expression to D and now check if nops is more than one, and if so, only now call select.

This is becuase nops(D(y)(x)) is one, while nops(diff(y(x),x) is two.

Is there a better way to do this, in order to avoid calling select and getting diff() ? I suppose I could also just check if the expression is exactly diff(y(x),x) before even calling select or has and avoid all this?

Worksheet attached

Download best_way_to_check.mw

Given

expr:=c[2]*sin(sqrt(3)*x/2) + c[3]*cos(sqrt(3)*x/2);
expr:=convert(expr,tan);

How to change the second result above (with the tan) back the the original form it was in?

I tried all different convert and simplification commands, and non managed to get back the original form.

convert(expr,sincos);
simplify(expr,size);
#etc...

Maple 2022.1 on windows 10