Saving data from nested for loop
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Hi
I want to store data from a nested for loop and this is my code
%%Initialisation 1
delta_x=(2*pi)/100;
delta_y=delta_x;
H=2*pi;
L=4*pi;
%Mesh
n=(L/delta_x)+1; Converts rectangle to a mesh
m=(H/delta_y)+1;
x=[0:delta_x:n]';
y=[0:delta_y:m]';
for i=x(2):delta_x:x(end-1)
for j=y(2):delta_y:y(end-1)
pointer=[(j-1)*n+i];
end
end
Everytime the pointer runs it only gives me the latest iteration and not all the iterations like I want. I tried putting (i,j) before it but that was to no avail and now am at my wits end as to what to do. Any help would be much appreciated
采纳的回答
Give this a shot. It's usually best to set up for-loops to iterate over integer values 1 to n. Those integer values can be used to index input values and store the outputs.
iLoop = x(2):delta_x:x(end-1);
jLoop = y(2):delta_y:y(end-1);
pointer = nan(numel(iLoop), numel(jLoop));
for i = 1:numel(iLoop)
for j = 1:numel(jLoop)
pointer(i,j)=(jLoop(j)-1)*n+iLoop(i);
end
end
3 个评论
Maaz Madha
2020-3-18
Adam Danz
2020-3-18
Good question!
This is known as preallocation. My example shows how to store scalar outputs (single value) at location (i,j) in variable 'pointer'. Instead of building that matrix as the loops iterate, the matrix is created with NaN values prior to the loops. This makes the code faster and cleaner.
The numel() function just returns the number of elements of a vector.
Maaz Madha
2020-3-18
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