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# 3-D Thermal Problem

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Yattapu Yaswanth on 8 May 2014
Closed: MATLAB Answer Bot on 20 Aug 2021
I'm working on my Home Work Problem, it took more than 9 weeks still I'm not able to solve. There are many errors, can anyone help me on this please and most important thing is I'M NEW TO MATLAB.
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Yattapu Yaswanth on 8 May 2014
how to preallocate for speed for a line "Ttot might be growing inside a loop. consider preallocating for speed" can you explain on this how to preallocate for speed
I have seen these errors for every line so can you explain in preallocating for speed for these type of issues

Star Strider on 8 May 2014
‘Preallocating for speed’ means creating a matrix of zeros before you calculate the elements of the matrix in a loop. The reason is that MATLAB can then simply fill the preallocated matrix in the loop, and not have to create memory space for each element as it is created. The ‘preallocating for speed’ isn’t an error, but a (quite valuable) suggestion.
For example without preallocating:
tic
for k1 = 1:500
for k2 = 1:500
A(k1, k2) = k1.^(k2/100);
end
end
toc
Elapsed time is 0.142800 seconds.
Preallocating:
A = zeros(500,500);
tic
for k1 = 1:500
for k2 = 1:500
A(k1, k2) = k1.^(k2/100);
end
end
toc
Elapsed time is 0.063392 seconds.
Even including the preallocation step in the time interval: Elapsed time is 0.066296 seconds.
So preallocating definitely saves time.