Trying to simultaneously solve the following, but I'm getting the following error, can someone please tell me how to fix it?

>> syms F

>> syms G

>> [F G]=solve('2*(F^2)*(G^2)+3*G=13.8','2*(G^3)+(F^2)=16.6')

The following is the error I get when I click enter:

Check for incorrect argument data type or missing argument in call to function 'solve'.

Answer 1

[chicken vector]

Try this syntax:

syms F G
eqn = [2 * F^2 * G^2 + 3 * G == 13.8 , 2 * G^3 + F^2 == 16.6];
sol = solve(eqn, [F G])

If you receive the error:

Undefined function 'sym' for input arguments of type 'char'

You don't have the Symbolic Math Toolbox and you need to install it.

Type ver in the command window to see the Toolboxes you have.

If you can't find the symbolic toolbox, type syms x in the command window and it will be suggested to you.

[Abdelrahman Ismail]

thank you so much for your answer.

I copy and pasted and got the following answer:

sol =

struct with fields:

F: [10×1 sym]

G: [10×1 sym]

It seems like it did not give me the values of F and G, which is what I want, unless I did something wrong?

[Torsten]

syms F G
eqn = [2 * F^2 * G^2 + 3 * G == 13.8 , 2 * G^3 + F^2 == 16.6];
sol = solve(eqn, [F G]);
vpa(sol.F)

ans = 

vpa(sol.G)

ans = 

[Abdelrahman Ismail]

Thank you good sirs/mams.

Appreciate it.

[Abdelrahman Ismail]

Hello, I am trying to do the same thing here:

>> syms P F

>> eqn = [1.3 * P - F^2.1 == 0 , P^1.6 - (900 - 95 * F)^0.5 + 10 == 0];

>> sol = solve(eqn, [P F]);

Warning: Possibly spurious solutions.

> In symengine

In mupadengine/evalin_internal

In mupadengine/feval_internal

In sym/solve (line 293)

what did I wrong this time? :/ followed the same code criteria.

[Torsten]

According to what MATLAB reports, the solution of your system of equations is parametrized by a value z_1 which is the solution of a polynomial equation of degree 168. So your system of equations has 2*168 = 336 solution pairs (P,F).

syms P F
eqn = [1.3 * P - F^sym('2.1') == 0 , P^sym('1.6') - (900 - 95 * F)^sym('0.5') + 10 == 0];
sol = solve(eqn, [P F],'ReturnConditions',1)

Warning: Possibly spurious solutions.

sol = struct with fields:
             P: [336×1 sym]
             F: [336×1 sym]
    parameters: [1×0 sym]
    conditions: [336×1 sym]

sol.P

ans = 

sol.F

ans = 

sol.conditions

ans = 

[Walter Roberson]

It is a category mistake to use solve() with floating point numbers. solve() is for finding closed form indefinitely precise solutions. For example solve(x^2 ==2) returns 2^(1/2) as a symbolic object, because the answer to the question is not 1.414 followed by any finite number of digits: if you take any finite number of digits and square the result you would not get 2.

What exactly does P^2.1 mean? Does it mean (P^4728779608739021)^(1/2251799813685248)? because that is how 2.1 is represented in double precision, as exactly 4728779608739021/2251799813685248 which is accurate to approximately 2^-52

[Abdelrahman Ismail]

Alright, thanks a lot! ill wrap my head around it and get it through.

[Torsten]

@Abdelrahman Ismail

I listed the solutions for your interest (see above).

If you want P and F to be real-valued, replace

syms P F

by

syms P F real

and you will only get one solution pair.

[Walter Roberson]

syms P F
eqn = [sym(13)/10 * P - F^(sym(21)/10) == 0 , P^(sym(16)/10) - (sym(900) - sym(95) * F)^(sym(5)/10) + sym(10) == 0];
sol = solve(eqn)
sol.P
sol.F

This produces two complex-valued solutions.

Representation matters for symbolic purposes.