GNU Octave

Time for action – using imagesc

1. Let us first consider a one dimensional problem with 20 grid points. The coefficient matrix is generated by calling cmat_1d:

   octave:5> A=cmat_1d(20);
   

2. To set the gray colour map, use (also see Chapter 3):

   octave:6> colormap("gray");
   

3. To make a scaled image of the matrix, we use:

   octave:7> imagesc(full(A))
   

   The result is shown in the left-hand side figure below.

What just happened?

Notice that in Command 7, we use the full matrix of A because imagesc does not currently support sparse matrices. It is easy to see that matrix elements indeed follow the matrix given by Equation (6.14).

For the two-dimensional problem, we can ...