Solving an equation with 2 known arrays

Question

Oded Ben Tsedek 2020-12-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/699365-solving-an-equation-with-2-known-arrays

回答： Sreeranj Jayadevan 2020-12-30

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I'm trying to solve equation with 1 variable (k) but 2 vectors (x and t).

I need to get an array of answers for k, such as (k[i] = eqn(t[i],x[i]).

This is what I wrote:

t = [28.35 53.34 85.39 132.7];
x = linspace(0.01,0.04,4);
k = sym ('k',[1 4]);
eqn = T-Ti==(2*q*sqrt((t.*k)/(c*p*pi))./k)*exp(((-x.^2)*c*p)./(4*k.*t))-((q*x)./k)*erfc(x/(2*sqrt((t.*k)/(c*p))));
solk = solve(eqn,k);
solk.k1
solk.k2
solk.k3
solk.k4

and of course it doesn't work.

How do I fix it?

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Answer 1

Sreeranj Jayadevan 2020-12-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/699365-solving-an-equation-with-2-known-arrays#answer_587233

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Your code is working as expected. I was able to execute the same when a different equation was used. Check if the equation you are using contain dimensional mismatches.

The following code works:

 x=sym('x', [1 4]);
 y=[1 2 3 4];
 z=[2 3 4 5];
 sol=solve(x.*y+z+1==0,x); % You can change this equation
 sol.x1
 sol.x2
 sol.x3
 sol.x4
 % Converting it into an array of type double
 temp=struct2cell(sol);
 sol_arr=double([temp{:}]);
 