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

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Sia
Sia 2015-4-28
评论： Sia 2015-4-29
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)

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采纳的回答

Philip Caplan
Philip Caplan 2015-4-29
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
  1 个评论
Sia
Sia 2015-4-29
Thanks man, the problem is my equations were not linear and I had to use iteration to solve it ;)

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