How do I make my for-loop control the signs (+/-) of two variables ("x1hat" and "x2hat") for each loop?

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Ludvig Engwall 2021-1-22

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https://ww2.mathworks.cn/matlabcentral/answers/724113-how-do-i-make-my-for-loop-control-the-signs-of-two-variables-x1hat-and-x2hat-for-each-lo

评论： Ludvig Engwall 2021-1-22

Depending on the signs of "x1hat" and "x2hat" i want the for-loop to calculate "W" differently. If "x1hat" and "x2hat" are of the same sign I want to calculate "W" in one way and if they are of different signs I want to calcutate "W" in another way. I tried my best to complete this with an "If-else-statement", but it doesnt look right in the plot..

Please help me with suggestion on how to improve the code. (asuming that all other variables are correctly defined)

[x1hat,x2hat]=deal(zeros(length(fv),1));
for n=1:length(fv)
    f=(fv(n))
    I=(Ihat(n))
    Fhat=I*BL
    A=[(-((2*pi*f)^2))*M+K]
    fhat=[Fhat;0]
    xhat=A\fhat
    x1hat(n)=xhat(1)
    x2hat(n)=xhat(2)
   if((x1hat(n)>=0 & x2hat(n)>=0)|(x1hat(n)<0 & x2hat(n)<0)) 
    W=(((2*p*pi^3)/c)*(f^4))*((abs(S1*x1hat(n))-abs(S2*x2hat(n)))^2)
   else
    W=(((2*p*pi^3)/c)*(f^4))*((abs(S1*x1hat(n))+abs(S2*x2hat(n)))^2)
   end
   W2=(((2*p*pi^3)/c)*(S1^2)*((Fhat^2)/(mA1+mspool)^2)*((f^4)/((((2*pi*f0)^2)-((2*pi*f)^2))^2)))
  plot(f,W,f,W2,'r*')
  xlabel('frequecie')
  ylabel('sound power')
  hold on;
end

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Answer 1

Jan 2021-1-22

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/724113-how-do-i-make-my-for-loop-control-the-signs-of-two-variables-x1hat-and-x2hat-for-each-lo#answer_603918

编辑：Jan 2021-1-22

A simplification:

if (x1hat(n) >= 0) == (x2hat(n) >= 0)
    ...
else
    ...
end

Avoid unnneded square brackets or parentheses.

Move repeated code outside the loop.

x1hat = zeros(length(fv), 1);
x2hat = zeros(length(fv), 1);
AxesH = axes('nextplot', 'on');
xlabel('frequecie')
ylabel('sound power')
for n = 1:length(fv)
    f = fv(n);
    I = Ihat(n);
    Fhat = I * BL;
    A = -((2 * pi * f)^2) * M + K;
    fhat = [Fhat; 0];
    xhat = A \ fhat;
    x1hat(n) = xhat(1);
    x2hat(n) = xhat(2);
    if (x1hat(n) >= 0) == (x2hat(n) >= 0)
        m = -1;
    else
        m = 1;
    end
    W  = (2 * p * pi^3/c) * f^4 * (abs(S1 * x1hat(n)) + m * abs(S2 * x2hat(n)))^2;
    W2 = (2 * p * pi^3/c) * (S1^2) * ((Fhat^2) / (mA1 + mspool)^2) * ...
         (f^4 / (((2*pi*f0)^2 - (2*pi*f)^2)^2));
    plot(AxesH, f, W, f, W2, 'r*');
end    