how to return the solution of a vector of variables one time instead of indexing sol.x1, solx2..etc

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Wazy sky 2018-11-12

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评论： Wazy sky 2018-11-14

Hi. For a system of linear equations, using solve fun, I want to return the solution for all the variables one time. with this function, I can call each solution by indexing which is not practical when I have many variables.

How could I call/return the solution for all the variables one time instead of indexing each variable individually, please?

I need to use the output solutions (solved variables) in another formula. see last 2 lines in the code where I used the for loop for this purpose.

for a large number of variables does not sound practical to call all the variables using the indexing: sol.f1, sol.f2, ...sol.fn for the solution of (f) vector of variables

Here is the code

k_tt=1; k_bt=-3.4744;k_tb=-3.4744;k_bb=18.5263;vp=0.3;
prompt={'a:','N:'};
title='Input';
answer=inputdlg(prompt,title);
a = str2double(answer{1});
N = str2double(answer{2});gam=zeros(N+1,N+1);delt=zeros(N+1,N+1);
A=zeros(N+1,N+1);B=zeros(N+1,N+1);C=zeros(N,N);D=zeros(N,N);Delta=zeros(N+1,1);Delta(1,1)=1;
for ii=0:N
    i2=ii+1;
    for jj=0:N
        jj2=jj+1;
        k=ii+jj;
        kk=mod(k,2);
        if kk==1
            gama=0;
        else gama=(4*(ii+1)*(jj+1))/((ii+jj+3)*(ii+jj+1)*(ii-jj+1)*(jj-ii+1));
        end
        gam(i2,jj2)=gama;
        if ii==jj
            delta1=1;
        else delta1=0;
        end
        delt(i2,jj2)=delta1;
        A(i2,jj2)=0.25*pi*(ii+1)*delta1+k_tt*a*gama;
        B(i2,jj2)=k_tb*a*gama;
        C(i2,jj2)=k_bt*a*gama;
        D(i2,jj2)=((3*(3+vp)*pi)/(4*(1+vp)))*(ii+1)*delta1*+k_bb*a*gama;
    end
end
f=sym('f',[N+1 1]);g=sym('g',[N+1 1]);
eqns=[A*f+B*g==(pi/2)*Delta,C*f+D*g==(pi/2)*Delta];
S=solve(eqns);
sol =vpasolve(eqns,[f;g]);
sol2=[S.f1;S.g1]; % this way works but I have to call all the variable indivdully! what if I have 100 variables ..i.e. f1...f100, do I need to use (sol.f1 all the way to sol.100)
% the reason is I need to use the solutions in another formula as below
h_1=0
for x=0:N
    h_1=h_1+(1+x)* *f(x,1);   %f(x,1) refers to the solved variables f1,f2,f3 ... I do not know how to call them here!
end

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Answer 1

Stephen23 2018-11-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/429367-how-to-return-the-solution-of-a-vector-of-variables-one-time-instead-of-indexing-sol-x1-solx2-etc#answer_346486

编辑：Stephen23 2018-11-12

在 MATLAB Online 中打开

You can dynamically access fieldnames:

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

For example:

S = vpasolve(...);
for k = 1:100
    F = sprintf('f%d',k);
    S.(F)
end

Another option is to use struct2cell and a comma-separated list:

S = vpasolve(...);
C = struct2cell(S);
V = [C{:}]

You can also use indexing into C to get specific values. You might also find orderfields and/or fieldnames useful (then you can sort the fields and select from fields that actually exist in the structure).

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Wazy sky 2018-11-14

Thanks Stephen Cobeldick

so much appreaciated

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