Unexpected, unexplained, difference between Matrix linear index and row and column subscripts

Good Morning;

writing a script I found myself discovering a difference i cannot explained.

for i=size(P,1)*size(P,2)
    if A(i)>1
        A(i)=1;
        B(i)=P(i).*(2./(gamma+1));
        C(i)=P(i)-(P(i)-B(i))./eta(type);
        D(i)=Q(i).*(C(i)./P(i)).^(gamma./(gamma-1));
        
        E(i)=sqrt(gamma.*R.*B(i));
        F(i)=E(i);
    end
end

writing the above code the end results were not as expected. i then wrote the same operations nesting 2 for cycles (row and column subscripts)

for i=1:size(P,1)
    for j=1:size(P,2)
        
        if A(i,j)>1
            A(i,j)=1;
            B(i,j)=P(i,j).*(2./(gamma+1));
            C(i,j)=P(i,j)-(P(i,j)-B(i,j))./eta(type);
            D(i,j)=Q(i,j).*(C(i,j)./P(i,j)).^(gamma./(gamma-1));
            
            E(i,j)=sqrt(gamma.*R.*B(i,j));
            F(i,j)=E(i,j);
        end
    end
end

this, strangely to me, gave me a different end result. I could not understand why.

A,B,C,D,E,F,P,Q 

are all matrices of same dimension and enter both cycles with same values, same goes for

gamma,eta, type

I would appreciate if someone would be able to explain the difference in the two methods, that should have behaved identically in my mind.

tips on more efficient/elegant ways of achieving the above are also welcome

Answer 1

[Bruno Luong]

Try to change

for i=size(P,1)*size(P,2)

to

for i=1:size(P,1)*size(P,2)

You light also learn to use debugger so such task.

[Jad Michele Samuel Musallam]

thanks to both.

well, that's embarassing. I never considered learning to use the debugger. Might consider now, thak you a lot

Answer 2

[Esen Ozbay]

You have forgotten to write 1: in the first line.

for i=size(P,1)*size(P,2) 

must be

for i = 1:size(P,1)*size(P,2)

You probably got 0's in all elements except one in the arrays you obtained.