# How would I write a code to solve a system of equations?

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Omar 2013년 10월 19일
답변: anjali wavhale 2020년 12월 1일
I need to solve a system of equations but I do not know the syntax for doing so. The equations are:
q1 = (1.53*10^-5)*t1^4 + (1.67*10^-2)*t1^3 + 6.85*t1^2 + 2746*t1 - 57793
q2 = 13.3*(t1-t2)
q3 = (1.53*10^-5)*t2^4 + (1.67*10^-2)*t2^3 + 6.85*t2^2 + 4846*t2 - 49161
also; q1=q2=q3
I'm new to MATLAB and not sure how to handle this many variables along with the scientific notation.
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Omar 2013년 10월 20일
I don't know what you mean exactly. How would you solve this in a non-mathematical way?

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### 답변(4개)

sixwwwwww 2013년 10월 20일
편집: sixwwwwww 2013년 10월 20일
Dear Omar, you can solve your system of equations using the following way:
t = sym('t%d', [1 2]);
q1 = 1.53e-5 * t(1)^4 + 1.67e-2 * t(1)^3 + 6.85 * t(1)^2 + 2746 * t(1) - 57793;
q2 = 13.3 * (t(1) - t(2));
q3 = 1.53e-5 * t(2)^4 + 1.67e-2 * t(2)^3 + 6.85 * t(2)^2 + 4846 * t(2) - 49161;
[solutions_t1, solutions_t2] = solve(q1 == q2 == q3, t(1), t(2))
Or
[solutions_t1, solutions_t2] = solve(q1 == q2, q2 == q3, t(1), t(2))
You can check which solutions are better because in first case you will get 4 solutions for both t1 and t2 and in second case you will get 16 solutions for both t1 and t2. I hope it helps. Good luck!
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sixwwwwww 2013년 10월 20일
You are welcome dear

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Walter Roberson 2013년 10월 20일
{q = 2003.839045, t1 = -819.5264017, t2 = -970.1909915},
{q = -10982.94224, t1 = -817.9943073, t2 = 7.790823431},
{q = 133.2164095, t1 = 20.04280634, t2 = 10.02653495},
{q = 13235.45859, t1 = 24.30348638, t2 = -970.8437757}
provided that you only want real-valued solutions.
This was done by substituting t1 for t(1) and t2 for t(2), and then plugging the three q equations into solve()
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David 2013년 10월 21일
편집: David 2013년 10월 21일
In addition to the answers already posted, be sure to put sym() around each of your equations. That is to say, do the following:
syms t1 t2
q1 = sym( 1.53e-5*t(1)^4 + 1.67e-2*t(1)^3 + 6.85*t(1)^2 + 2746*t(1) - 57793 );
q2 = sym( 13.3*(t(1) - t(2)) );
q3 = sym( 1.53e-5*t(2)^4 + 1.67e-2*t(2)^3 + 6.85*t(2)^2 + 4846*t(2) - 49161 );
[solutions_t1, solutions_t2] = solve(q1 == q2, q2 == q3, t1, t2);
solve requires that your equations be symbolic objects which is guaranteed by using sym().
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David 2013년 10월 22일
Oh? This seemed to correct a problem I was having earlier in using the solve function. You actually saw that question and made useful suggestions, though suggestions that did not quite do the trick. Maybe we are both missing something or maybe it's just me...

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anjali wavhale 2020년 12월 1일
how to do least square estimation for system with the prbs as input to it

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