how to prevent overwriting in matrix while creating in for loop?

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swarnali mukhopadhyay 2016-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/316388-how-to-prevent-overwriting-in-matrix-while-creating-in-for-loop

编辑： Stephen23 2016-12-11

T(1,1) = (a-b-c);
T(1,2)=b;
T(2,1) = c;
C(1) = a*To;
for j= 2:1:nx-1
    i=1;
%middle nodes
T(i,j-1) = b/2;
T(i,j) = 2*a-b-2*c;
T(i,j+1) = b/2;
T (i+1,j+1) = 2*c;
C(j) = 2*a*To;
   T(i,j)=0;
end
%end node
T(1,nx-1) = b;
T(1,nx) = b + c + a;
T(2,nx) = c;
C(nx) = a*To;
%sliding
for i = 2:1:nysl
for j= 2:1:nx
 if(i<=nysl-1 && j==1);
    T(i-1,j)=1;
    T(i,j)= -4;
    T(i+1,j)=1;
    T(i,j+1)=2;
elseif (i<=nysl-1 && j<=nx-1);
    T(i-1,j) =1;
T (i,j-1) =1;
T(i,j) =-4;
T(i,j+1)= 1;
T(i+2,j)=1;
elseif (i<=nysl-1 && j==nx);
T(i-1,j) =1;
T (i,j-1) =2;
T(i,j) =-4;
T(i+1,j)= 1;
   else
   T(i,j)=0;
 end
end
end

while creating the matrix the successive operation overwrites the values allocated previously.Is there anyway to void the overwriting?

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Stephen23 2016-12-11

编辑：Stephen23 2016-12-11

"Is there anyway to avoid the overwriting?"

Yes. Simply preallocate an output array of the correct size, and use indexing to assign the new values within the loop. You will find lots of examples online.

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