how to solve the expression using the loops

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phoenix 2017-12-14

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https://ww2.mathworks.cn/matlabcentral/answers/372964-how-to-solve-the-expression-using-the-loops

编辑： Jan 2017-12-18

p=0;
q=0;
pr=0;
qr=0;
a=0;
b=0;
ar=0;
br=0;
for x=1:1:5
    p=p+P(x,1);
    q=q+Q(x,1);
    pr=pr+P(x,1)*5^(x-1);
    qr=qr+Q(x,1)*5^(x-1);
end
for x=1:1:15
    a=a+A(x,1);
    b=b+B(x,1);
    ar=ar+A(x,1)*5^(x-1);
    br=br+B(x,1)*5^(x-1);
end

Now,how to find this: p*qr*b+p*br*q; combining the two loops.

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Jan 2017-12-14

What are P and Q, A and B? What's wrong with p*qr*b+p*br*q ?

phoenix 2017-12-14

编辑：phoenix 2017-12-14

matrices.if i write in this form p*qr*b+p*br*q ,is it right? how can i combine these two different loops into a single one?

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Answer 1

Jan 2017-12-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/372964-how-to-solve-the-expression-using-the-loops#answer_296285

编辑：Jan 2017-12-16

在 MATLAB Online 中打开

What about:

for x=1:5
  p  = p + P(x,1);
  q  = q + Q(x,1);
  pr = pr + P(x,1)*5^(x-1);
  qr = qr + Q(x,1)*5^(x-1);
  a  = a + A(x,1);
  b  = b + B(x,1);
  ar = ar + A(x,1)*5^(x-1);
  br = br + B(x,1)*5^(x-1);
end

"Combining" seems to be easy, because the two loops are independent from each other. You could even omit the loops:

    c  = 5 .^ (0:4).';     % [EDITED] transposed
    p  = sum(P(1:5, 1));
    q  = sum(Q(1:5, 1));   % [EDITED] trailing parenthesis added
    pr = sum(P(1:5,1) .* c);
    qr = sum(Q(1:5,1) .* c);

And the same for the 2nd loop.

If p*qr*b+p*br*q is correct or not depends on what you want as output. Simply try it. Maybe you want the elementwise products:

p .* qr .* b + p .* br .* q

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Jan 2017-12-16

编辑：Jan 2017-12-16

在 MATLAB Online 中打开

@Phoenix: I cannot run your code, because I do not have your inputs. "It does not work" does not allow to reconsider, what's going on, when you run it. It is not clear, what the problem with "combining" is, because it seems to be trivial to join the bodies of the two independent loops. If you need further help, please explain, what the problem is now.

But when I guess:

P = rand(5, 1);
Q = rand(5, 1);
A = rand(5, 1);
B = rand(5, 1);
p=0; q=0; pr=0; qr=0;
a=0; b=0; ar=0; br=0;
for x = 1:5
  p  = p + P(x,1);
  q  = q + Q(x,1);
  pr = pr + P(x,1) * 5^(x-1);
  qr = qr + Q(x,1) * 5^(x-1);
end
for x = 1:5
  a  = a + A(x,1);
  b  = b + B(x,1);
  ar = ar + A(x,1) * 5^(x-1);
  br = br + B(x,1) * 5^(x-1);
end
R1 = p * qr * b + p * br * q
c  = 5 .^ (0:4).';
p  = sum(P(1:5, 1));
q  = sum(Q(1:5, 1));
pr = sum(P(1:5, 1) .* c);
qr = sum(Q(1:5, 1) .* c);
R2 = p * qr * b + p * br * q

Now R1 and R2 have the same values. Do you want something else?

But a,b,ar,br do not occur in the wanted formula at all. Strange.

phoenix 2017-12-18

@Jan Simon: What does this symbol .' stand for used in c = 5 .^ (0:4).';?

Jan 2017-12-18

编辑：Jan 2017-12-18

@phoenix: .' is the transpose operator. It is frequently confused with ' , but this is the complex conjugate transposing. See https://www.mathworks.com/help/matlab/ref/transpose.html and https://www.mathworks.com/help/matlab/matlab_prog/matlab-operators-and-special-characters.html

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how to solve the expression using the loops

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