solving 5 nonlinear equations

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I want to solve five nonlinear equations for five unknowns. How to solve in matlab?
The equations are-
32.5=2*sqrt((a*b-e^2)/(a*((1/c)+2/(sqrt(a*b)+e))))
81=2*sqrt(sqrt((a^2-d^2)/(b((2/(a-d))+(2/(a+d)))))*(sqrt((a*b-e^2)/(a*((1/c)+2/(sqrt(a*b)+e))))))
230=b-(2*e^2/(a+d))
0.3=(b*d-e^2)/(b*a-e^2)
0.3=e/(a+d)
Thanks.

采纳的回答

Star Strider
Star Strider 2017-7-9
If you have the Symbolic Math Toolbox, this will give you one set of solutions:
syms a b c d e
Eqns = [32.5 == 2*sqrt((a*b-e^2)/(a*((1/c)+2/(sqrt(a*b)+e))));
81 == 2*sqrt(sqrt((a^2-d^2)/(b*((2/(a-d))+(2/(a+d)))))*(sqrt((a*b-e^2)/(a*((1/c)+2/(sqrt(a*b)+e))))));
230 == b-(2*e^2/(a+d));
0.3 == (b*d-e^2)/(b*a-e^2);
0.3 == e/(a+d)];
[as,bs,cs,ds,es] = vpasolve(Eqns, [a,b,c,d,e])
All the solutions are complex, so they may have complex-conjugate solutions as well. I will leave you to explore those.
  4 个评论
Walter Roberson
Walter Roberson 2017-7-10
编辑:Walter Roberson 2017-7-10
For example, if the final 0.3 were really 0.31 then the solution would change from
a = 259.1635046015543, b = 295.7619655879812, c = 1.064584012228195, d = 106.1807486650092, e = 109.6032759799690
to
a = 262.1789467186743, b = 301.4328240934383, c = 1.058495937853918, d = 109.4798675031687, e = 115.2142324087714
If you let the final 0.3 be 0.3+delta for some delta presumably in the range -0.05 to +0.05 (that is, you assume 0.3 is a rounded value instead of 3/10 exactly), then the final solution involves large numbers multiplied by powers of delta up to delta^50. For abs(delta) < 1 those terms get very small, but this gives you an ideal of how very important it is to not attempt to find exact solutions to equations that involve floating point numbers.
Alex Sha
Alex Sha 2024-11-20
This is an interesting problem. Try some case below:
1: Taking "3/10' as "-10", real number solution:
a: -1116.42814745858
b: -0.14494811265632
e: 11.5072474056132
c: -12.0995087597244
d: 1115.27742271802
2: Taking "3/10' as "-5", real number solution:
a: 616.406269419948
b: 1.27542919070194
e: 22.8724570809345
c: -26.5477709060796
d: -620.980760836136
3: Taking "3/10' as "0", real number solution:
a: 210.846823805096
b: 230
e: -5.50683766803909E-161
c: 1.16019523942894
d: 1.05335763282267E-160
4: Taking "3/10' as "0.1", real number solution:
a: 214.022434088449
b: 234.751776376541
e: 23.7588818827026
c: 1.148178022009
d: 23.5663847385774
5: Taking "3/10' as "0.2", real number solution:
a: 226.651538558968
b: 252.564957781941
e: 56.4123944548472
c: 1.11542080793499
d: 55.4104337152429
6: Taking "3/10' as "0.35", real number solution:
a: 291.915645771019
b: 337.717161812537
e: 153.881659732203
c: 1.03363195571106
d: 147.746239178151
7: Taking "3/10' as "0.5", real number solution:
a: 852.513827599216
b: 1023.08265336835
e: 793.08265336835
c: 0.926592791567609
d: 733.651479137491
8: Taking "3/10' as "1.5", real number solution:
a: 29.7882470501465
b: 20.1947124949364
e: -69.935095835023
c: -1.99496910118526
d: -76.4116442734963
9: Taking "3/10' as "3.5", real number solution:
a: 257.625789918568
b: 2.26431063362606
e: -32.5336699094821
c: 4.31690559130787
d: -266.92112417842
10: Taking "3/10' as "5.0", real number solution:
a: 409.404208509883
b: 0.853441216192337
e: -22.9146558784191
c: 2.11844107695153
d: -413.987139685574

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