Find a row in a matrix

Hi!

I have a generic matrix with random numbers (-1 and +1).

M=[ 1 -1  1 -1
    1  1  1 -1
   -1  1 -1  1 % <----- this row
    1  1 -1  1];

How can I extract a row index?

a=[-1  1 -1  1];
idx=3;

Thank you

Answer 1

[Rik]

Assuming you have that vector already:

M=[ 1 -1  1 -1
    1  1  1 -1
   -1  1 -1  1 % <----- this row
    1  1 -1  1];
a=[-1  1 -1  1];

tmp=abs(M-a);%uses implicit expansion, works in R2016b and newer
tmp=sum(tmp,2) <= eps;
idx=find(tmp);