for loop with multiple indices

i want to write a function that goes through each row of a matrix and at the same time go through each element of the first row, what i had in mind was something like this

function X1= RREF_GEN (X,M,N)
for m = 2:M , n = 1:N;
    X1=X(m,:)-(X(m,n)/X(1,n))*X(1,:);
end

this doesn't work, and nesting doesn't either because i want the two loops to run at the same time not one after the other

please help

Answer 1

[Walter Roberson]

That is not possible for the general case where N is not the same as (M-1) -- that is, if the two variables to be incremented do not have the same length.

If the two did have the same length then

m_vals = 2:M;
n_vals = 1:N;
for idx = 1 : length(m_vals)
   m = m_vals(idx);
   n = n_vals(idx);
   X1=X(m,:)-(X(m,n)/X(1,n))*X(1,:);
end

or

for m = 2 : M
  n = m - 1;
  X1=X(m,:)-(X(m,n)/X(1,n))*X(1,:);
end

or

for m = 2 : M
    X1=X(m,:)-(X(m,m-1)/X(1,m-1))*X(1,:);
end