# solve function give a wrong solution

6 visualizaciones (últimos 30 días)
Adriano el 23 de Jul. de 2020
Respondida: John D'Errico el 23 de Jul. de 2020
Hi all,
I'm trying to solve a simple equation in Matlab using solve function. The code is:
syms x
solv = solve( (1+x/12)^12 == 1.02)
The solution is 0.0204 however Matalb give me this solution:
solv =
- (6*50^(11/12)*51^(1/12))/25 - 12
(6*50^(11/12)*51^(1/12))/25 - 12
- (50^(11/12)*51^(1/12)*6i)/25 - 12
(50^(11/12)*51^(1/12)*6i)/25 - 12
- (6*50^(11/12)*51^(1/12)*(3^(1/2)/2 - 1i/2))/25 - 12
(6*50^(11/12)*51^(1/12)*(3^(1/2)/2 - 1i/2))/25 - 12
- (6*50^(11/12)*51^(1/12)*(3^(1/2)/2 + 1i/2))/25 - 12
(6*50^(11/12)*51^(1/12)*(3^(1/2)/2 + 1i/2))/25 - 12
- (6*50^(11/12)*51^(1/12)*((3^(1/2)*1i)/2 - 1/2))/25 - 12
(6*50^(11/12)*51^(1/12)*((3^(1/2)*1i)/2 - 1/2))/25 - 12
- (6*50^(11/12)*51^(1/12)*((3^(1/2)*1i)/2 + 1/2))/25 - 12
(6*50^(11/12)*51^(1/12)*((3^(1/2)*1i)/2 + 1/2))/25 - 12
>> round(solv)
ans =
-24
0
- 12 - 12i
- 12 + 12i
- 22 + 6i
- 2 - 6i
- 22 - 6i
- 2 + 6i
- 6 - 10i
- 18 + 10i
- 18 - 10i
- 6 + 10i
Why it happen? Someone can help me? Thanks!
##### 1 comentarioMostrar -1 comentarios más antiguosOcultar -1 comentarios más antiguos
KSSV el 23 de Jul. de 2020
Why do you think is wrong?

Iniciar sesión para comentar.

Vladimir Sovkov el 23 de Jul. de 2020
syms x
solv = double(solve( (1+x/12)^12 == 1.02))
There are many solutions. The one you are interested in is rather 0.0198189756230421 but not 0.0204.
##### 1 comentarioMostrar -1 comentarios más antiguosOcultar -1 comentarios más antiguos
Adriano el 23 de Jul. de 2020
Sorry I understood...the solutions are correct!

Iniciar sesión para comentar.

### Más respuestas (1)

John D'Errico el 23 de Jul. de 2020
Using round to convert those results is wrong. Instead use either double or vpa to do so, depending on whether you want a symbolic or double precision answer. Thus we see:
digits 20
>> vpa(solv)
ans =
-24.019818975623042098
0.019818975623042097611
- 12.0 - 12.019818975623042098i
- 12.0 + 12.019818975623042098i
- 22.40946858177980274 + 6.0099094878115210488i
- 1.5905314182201972597 - 6.0099094878115210488i
- 22.40946858177980274 - 6.0099094878115210488i
- 1.5905314182201972597 + 6.0099094878115210488i
- 5.9900905121884789512 - 10.40946858177980274i
- 18.009909487811521049 + 10.40946858177980274i
- 18.009909487811521049 - 10.40946858177980274i
- 5.9900905121884789512 + 10.40946858177980274i
The second solution is apparently the one you wanted, as has already been shown.
##### 0 comentariosMostrar -2 comentarios más antiguosOcultar -2 comentarios más antiguos

Iniciar sesión para comentar.

### Categorías

Más información sobre Numeric Solvers en Help Center y File Exchange.

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by