Substituting NaN values of one matrix to another?

Hello, I have two matrices of equal dimensions. In one matrix I have set a threshold value, over which the cells are set to NaN. If possible, I would like to set the same i,j cells of the second matrix to NaN as well, essentially using the first matrix as a "mask." Is this possible? Any advice you can provide would be appreciated! Thanks, Nikki

Answer 1

[James Tursa]

a = first matrix with NaN values
b(isnan(a)) = nan;

Answer 2

[Thomas]

Some thing like this;

a=[1 2 3;4 1 0 ;1 3 8]
b=[4 5 6; 7 8 9; 1 2 3]
b(a>3)=NaN;   % anything above 3 in a becomes NaN in b
a(a>3)=NaN;   % anything above 3 in a becomes NaN in a

a 
b