error using / matrix dimensions must agree

Hello,

while running my programme i am getting an error message of error using / matrix dimension in following code.

After changing / to ./ form it is giving error message A(I)=B dimension of A and B must agree.

if i==n_oriff
           if P(i-1,j)>=P(i,j)
               b(i)=.3*.25*sqrt( 2*Cpf(i)/R*P(i-1,j)*P(i-1,j)/R/T(i-1,j)*((P(i,j)/P(i-1,j))^(2-2*R/Cpf(i))-(P(i,j)/P(i-1,j))^(2-R/Cpf(i))))+0.1*mdotn(i-1,j);
           else
               %b(i)=.3;
                b(i)=-.3*.25*sqrt(2*Cpf(i)/R*P(i,j)*P(i,j)/R/T(i,j)*((P(i-1,j)/P(i,j))^(2-2*R/Cpf(i))-(P(i-1,j)/P(i,j))^(2-R/Cpf(i))))+0.1*mdotn(i-1,j);
           end
end

please anyone help me...

thanks in advance.....

[Walter Roberson]

We need to know size(i), size(j), size( R)