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for loop

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rami
rami 2012-4-1
Hi
I have matrix M(3,3)
I need to solve this equation
for i=1:3
for j=1:3
for k=1:3
bi,j,k=(1/2)*(diff(M(k,j),theta1)+diff(M(k,i),theta1)-diff(M(i,j),theta1))
end
end
end
I need to have the answers in form
b111
b112
b121
....
b333
how i can do that thx

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采纳的回答

Walter Roberson
Walter Roberson 2012-4-1

更多回答（3 个）

Andrei Bobrov
Andrei Bobrov 2012-4-1
eg
syms x
M = [x^4,2,x^(4/5)-4*x;x,2*x^3,log(x);exp(3*x),x,3*x];
solution
dM = diff(M,x);
idx = fliplr(fullfact(size(M,1)*ones(3,1)));
id = cellfun(@(x)sub2ind(size(M),idx(:,x(1)),idx(:,x(2))),{[3 2],[3 1],[1 2]},'un',0);
b = 1/2*(dM(id{1}) + dM(id{2}) - dM(id{3}));
ADD on Rami comment
eg
syms x y z
M = [x^4*z-y,z*2,x*z^(4/5)-4*x*y;x,2*z*y*x^3,log(x)/y;z*exp(3*x)-y,z*x*y^2,z*(y-z^3)*3*x];
theta = [x y z];
solution
dM = arrayfun(@(ii)diff(M,theta(ii)),1:numel(theta),'un',0);
dM = cat(3,dM{:});
[k j1 i1] = ndgrid(1:numel(theta));
id = {i1(:) j1(:) k(:)};
s = [3 2 1;3 1 2;1 2 3];
idx = cell2mat(arrayfun(@(x)sub2ind(size(dM),id{s(x,:)}),1:3,'un',0));
b = dM(idx)*[1;1;-1]/2
OR variant with loop for..end
for i1=1:3
for j1=1:3
for k=1:3
b1(i1,j1,k) = (1/2)*(diff(M(k,j1),theta(i1))...
+diff(M(k,i1),theta(j1))-diff(M(i1,j1),theta(k)));
end
end
end
b_ijk = reshape(permute(b1,[3 2 1]),[],1)
  1 个评论
rami
rami 2012-4-1
Thx for your answer:
In the solution I can not know
b111
b112
b121
b122
...etc
and in my example I want to make some modify that there are 3 variables theta1, theta2, theta3
for i=1:3
for j=1:3
for k=1:3
bijk=(1/2)*(diff(M(k,j),theta(i))+diff(M(k,i),theta(j))-diff(M(i,j),theta(k)))
end
end
end
So i want to find the values
b111
b112
........

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Image Analyst
Image Analyst 2012-4-1
Change "bi,j,k" to "b(i,j,k)"
  2 个评论
rami
rami 2012-4-1
Thx
I try but wasn't useful
Image Analyst
Image Analyst 2012-4-2
Well like Andrei and I both suggested, you should use a 3D matrix and not individually named variables. In fact the answer you accepted, Walter's, also recommends using an indexed matrix and recommends against using what you say you wanted. So we're left confused. But whatever.....as long as you got something you like, even though it's not recommended.

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rami
rami 2012-4-1
thx The link was so useful and the answer will be for one variable
for i=1:3 for j=1:3 for k=1:3
eval(sprintf('b%d%d%d= (1/2)*(diff(M(k,j),theta1)+diff(M(k,i),theta1)-diff(M(i,j),theta1))', i,j,k));
end
end
end

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