Solving equations in a for loop with changing variables

Question

Samantha Andeson 2020-10-30

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https://ww2.mathworks.cn/matlabcentral/answers/631724-solving-equations-in-a-for-loop-with-changing-variables

评论： Samantha Andeson 2020-10-31

Hi all,

Not very experienced with matlab and trying to solve for d, L, and H as a function of x changing. The assignment asks that for the first half of x, H=0.5 and d=1.9 but I haven't been able to figure out how to start the loop in the middle of those vectors. I hardcoded a little bit to try to troubleshoot my first line, but the loop skews my depth somehow. Any advice would be greatly appreciated!

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Stephan 2020-10-30

please insert your code - we can not copy a code from a picture...

Samantha Andeson 2020-10-31

My apologies

x=linspace(0,50,500);

d=zeros(length(x),1);

H=zeros(length(x),1);

L=zeros(length(x),1);

%d(1:length(x)/2)=1.9;

%H(1:length(x)/2)=0.5;

H(1)=0.5; d(1)=1.9;

d(2)=d(1)-(S.*x(2)); %this is what I'm trying to make the first line

d(3)=d(2)-(S.*x(3)); %of my loop do

d(4)=d(3)-(S.*x(4));

X=x(:);

if H/d>0.8

for i=1:length(X)

d(i)=d(i)-(S.*X(i)); %1 column matrix

k(i)=getwavek(1/T,d(i)); %1 row matrix

L(i)=(2*pi)./(k(i)); %1 column matrix

n(i)=1/2.*(1+((2.*k(i).*d(i))/(sinh(2.*k(i).*d(i))))); %1 row matrix

N(i)=n(:); %Thought this would help by "index exceeds # of array elements" error

H(i)=H(i-1)./sqrt((N(i).*L(i))./(N(i-1).*L(i-1))); %This is my problem

end

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Answer 1

Juan Sagarduy 2020-10-30

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https://ww2.mathworks.cn/matlabcentral/answers/631724-solving-equations-in-a-for-loop-with-changing-variables#answer_529639

Hi Samantha The first line in your code in the loop is not correct. It should d(i)=d(i-1)-S.*x(i). But then the loop must start with i=2. Otherwise, MATLAB would throw an error. Good luck / Juan