how to use the output of 'solve' in another equation

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omnia 2011-12-5

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https://ww2.mathworks.cn/matlabcentral/answers/23047-how-to-use-the-output-of-solve-in-another-equation

Hi everyone I used 'solve' function to solve an equation and got a variable 'v' then I converted it to double. The problem is when I wrote two equations with two variables x and y which contain v as a constant, I did not get the values of x and y but instead a symbolic expression in v. How can I make the program substitute with the value of v I already got from the first step. v=double(solve('3*v/5+v+8')); S=solve('x+y=1','x-11*y=-v'); yield a solution in v S.x=11/12-1/12*v S.y=1/12*v+1/12

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Walter Roberson 2011-12-5

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

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Answer 1

Walter Roberson 2011-12-5

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https://ww2.mathworks.cn/matlabcentral/answers/23047-how-to-use-the-output-of-solve-in-another-equation#answer_30279

在 MATLAB Online 中打开

Sx = double(subs(S.x, 'v', v));
Sy = double(subs(S.y, 'v', v));

However, it would be shorter if you used

syms x y
[Sx Sy] = double( solve('3*v/5+v+8', 'x+y=1','x-11*y=-v', x, y) );

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omnia 2011-12-5

Thanks very much

omnia 2011-12-5

when I did 'S.x' in my program I had very long expression (after using simplify)in the form of numerator and denominator as a function of v -although it can be written in much simpler form. when i did 'subs(S.x, 'v', v)' i have NAN.

How can I make the program write it in a simpler way (using 1.2*10^34 for example instead of writing at as 33 number)??

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