Nested For Loops Array Indexing
显示 更早的评论
Hi,
I'm trying to optimize a piece of code by allocating a matrix to zeros initially, rather than resetting the value each time in the for loop. The aim of this is to make the for loop run faster and sum the T and D variables.
I have simplified my code to:
endtime=200;
for time=1:endtime
for i=1:6
for j=1:6
for k=1:6
for p=1:6
D(i*j*k,time)=D(i*j*k,time)+otherfunctions(i,p,k);
end
T(i+1,time)=T(i+1,time)+D(i*j*k,time)*qd(k,time)*qd(j,time);
end
end
end
end
I would like to reset the value of D every time the k loop is entered. I know this can be achieved through just setting D=0 after "T(i+1,time)=...." however this would be done 6^3 * endtime times. Surely it would be more efficient to allocate D as a matrix of zeros initially and then cycle through the D matrix. I've tried to do this through D(i*j*k,time) but obviously I get the same array index for different values of i, j and k because their product is the same but their sequence is different. Can anybody help me?
采纳的回答
Adam
2014-12-12
idx = sub2ind( [6 6 6], i, j, k);
D( idx, time ) = ...;
will allow you to make best use of indexing into D without over-writing values or leaving massive gaps in the matrix.
更多回答（1 个）
If you don't need the various D values for the different times, you can use
for time ...
for i ...
for j ...
D = 0;
for k ...
D = D + otherfunctions(i,p,k);
end
T(i+1,time)= ... + D + ...
end
end
end
If you have to save values of D for different times, use D(time) instead of D.
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
Translated by 
