# How to solve equation with "Error using symengine A square matrix is expected",

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friet 2017년 4월 8일
댓글: friet 2017년 4월 8일
Hello
My code below written to solve an equation works well with a single input parameter d (line 8). However, when I have a vector for the input "d" as shown in line 9, Matlab complain that I have "symengine". here is my code.Any help is appreciated.
clear all
clc
close all
% definition of constants
Y=9*10^(-13);
% d=20*10^-3;
d= linspace(1*10^-3,20*10^-3,10);
q=1.6*10^(-19);
kB=4.0434e-21;
er=2.8320e-11;
mp=1*10^-9;
mn=1*10^-9;
c=3.2520e+23;
kr=q*(mp+mn)/(er);
no=Y/(q*(mp+mn));
kdo=kr*no*no/c;
Lb= (q^2)/(8*pi*er*kB);
syms Vs
b=(Lb*q*(Vs./d))./(kB );
num=besselj(1,sqrt(-8*b));
den=sqrt(-2*b);
Fb=num./den;
kd=kdo*Fb;
eqn = (((kd*kr*c)^0.5).*d.^2)./(mp+mn)==Vs;
solVs = solve(eqn,Vs);
vpa(solVs)

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### 채택된 답변

Walter Roberson 2017년 4월 8일
eqn = (((kd*kr*c).^0.5).*d.^2)./(mp+mn)==Vs;
Notice the .^ instead of ^
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friet 2017년 4월 8일
Thanks!

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