Getting Complex numbers for a (2equation+2unknown)

Hi All

I am wondering why I am getting complex numbers for this code, any help would be really appreciated.

clear
clc
close all

syms sigma a

a0=0.01;
w=0.05;

% defining the equations

F=0.265*(1-(a/w))^4 +(0.857+0.265*(a/w))*((1-(a/w))^(-3/2));
Kapp=sigma*sqrt(3.14*a)*F;
KC=110000000;
KR=KC*(4-3*exp(-(a-a0)/0.003));
diffKapp = diff(Kapp,a)
diffKR = diff(KR,a)

%solving the equations
[S, avalue] = solve([Kapp == KR, diffKapp == diffKR], [sigma, a])

double(S)
double (avalue)

Answer 1

[Philip Caplan]

You can ensure 'sigma' and 'a' are treated as real variables by declaring them slightly differently. Instead of

syms sigma a

please use

sigma = sym('sigma','real');
a = sym('a','real');

For more information on setting assumptions for symbolic variables, please see

http://www.mathworks.com/help/symbolic/sym.html#zmw57dd0e112213

[Sia]

Thanks man, the problem is my equations were not linear and I had to use iteration to solve it ;)