1d_stencil codes all have wrong factor

[stevenrbrandt]

All the 1d_stencil codes have a line that looks like this:
return middle + (k * dt/dx * dx) * (left - 2*middle + right);
The code should look like this:
return middle + (k * dt/(dx * dx)) * (left - 2*middle + right);

Because the example codes all have dx set to 1, fixing the
expressions won't make any difference for output. However,
if dx is set to any other value the results will be wrong.

[Titzi90]

You are absolutely right