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

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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

Bruno Luong on 26 Oct 2021
Edited: Bruno Luong on 26 Oct 2021
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.
Edited: Jad Michele Samuel Musallam on 26 Oct 2021
thanks to both.
well, that's embarassing. I never considered learning to use the debugger. Might consider now, thak you a lot

Esen Ozbay on 26 Oct 2021
Edited: Esen Ozbay on 26 Oct 2021
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.

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