How to do Matrix calculations IF certain conditions are present.

Question

Jonathan Pulman 2013-6-22

I have 2 matrices A and B and want to do A./B But some values in B are zero, producing inf then, in later calculations, NaN.

I think I can find the zero values using a logical matrix (learning it!) but I don't know how to use that information.

How do I do; If value_in_matrix_B is not zero, do A./B

Or more generally, how do I do IF such_and_such_condition applies to a particular position THEN do That;

Jonathan.

Answer 1

Walter Roberson 2013-6-23

value_in_matrix_B = B(J,K);
if value_in_matrix_B ~= 0
   A ./ value_in_matrix_B
end

If you are talking about doing this using logical indexing, then:

nzB = B ~= 0;
A(nzB) ./ B(nzB)

but what about the places where it is 0 ?