@acer 

I teach a Linear algebra course; introducing matrices, I would show that pictures "are" matrices, so the best way I think is to show  matrix and image together. "Compare" means "to see them together".

@acer 

Nice.

Yes, actually I need just to compare a 0..1 matrix (black and white)

M:=RandomMatrix(8,generator=0..1);

or a 0..255 matrix (gray scale 8 bits)

M:=RandomMatrix(8,generator=0..255);

with the corresponding pixel-plot. 

P.S. Please, how do you write in Maple notation?

@dharr 

The command matrixplot is perfect, because I do not need any image!

Could I get a grayscale, from white (0) to black (255)?

@dharr You are right

@Carl Love 

A[..,-[$n]];
Error, invalid `$` operator
      Typesetting:-mambiguous(A(period;&periodcommauminus0

        (Typesetting:-mambiguous(dollarn, 

        Typesetting:-merror("invalid `$` operator")))))

A[-[$n]];
Error, invalid `$` operator
 

@Carl Love Sure, sorry

I am really a beginner ...

Thats is very useful for my work, thanks!

Thanks, that is exactly what I want, even if I am not able to understand the command

U:=U[..,p]

But I have learned the magic function "fnormal", thanks!

Just a question more:
can I get the (real) eigenvalues (and therefore the correspondig eigenvector) in decreasing order?

It works, thanks!

My matrix is a covariance matrix, so I cannot add the option shape=symmetric.

Thanks, they works!

For some reasons I need to name my variables x[1], x[2], ...

What if I don't know how many variables for the function f? That is, could I generalize the definition of Gf without knowing a priori how many variables there are?

@Preben Alsholm 

Right, thank you

@Preben Alsholm please, could you explain me what is "Maple notatio a.k.a., 1D input" and how can I set it? Thanks

Why crash and not an error message?  Moreover, look at this: why 22?

Download edges.mw