# Solution of electric circuit- result from ilaplace in complex form

2 views (last 30 days)
john on 19 Mar 2014
Commented: john on 23 Mar 2014
Hello,
I solve electric circuit with resistors, inductor, kapacitors a sources.
In final step, I need make ilaplace to obtain result in time domain. But I got result in complex form. I do not know, what can I do. For example:
ilaplace(vpa(simple(-(17000*2^(1/2)*s^3 + (5100000*2^(1/2) + 5338000*6^(1/2))*s^2 + (34000000000*2^(1/2) + 1601400000*6^(1/2))*s + 10676000000000*6^(1/2))/((s^2 + 98596)*(7*s^3 + 19600*s^2 + 25200000*s + 20000000000)))))
ans=2.2002148818154076690682970002036/exp(1668.6981733835695764475415844609*t) + exp(314.0*t*i)*(2.2968284526268184064188098725796*i - 0.39524760709456610146639250224196) + exp(t*(- 1179.9312491214260645340516852799*i - 565.65091330821521177622920776954))*(0.37373997606394535632565131956824*i - 0.70485983381313773306775599785985) + exp(t*(1179.9312491214260645340516852799*i - 565.65091330821521177622920776954))*(- 0.37373997606394535632565131956824*i - 0.70485983381313773306775599785985) + (1/exp(314.0*t*i))*(- 2.2968284526268184064188098725796*i - 0.39524760709456610146639250224196)
or:
>> vpa(ilaplace(simplify(-(17000*2^(1/2)*s^3 + (5100000*2^(1/2) + 5338000*6^(1/2))*s^2 + (34000000000*2^(1/2) + 1601400000*6^(1/2))*s + 10676000000000*6^(1/2))/((s^2 + 98596)*(7*s^3 + 19600*s^2 + 25200000*s + 20000000000)))))
3.11/exp(1699.0*t) - 6.5*sin(314.0*t) - 1.12*cos(314.0*t) + exp(t*(- 1200.0*i - 566.0))*(0.529*i - 0.997) + exp(t*(1200.0*i - 566.0))*(- 0.529*i - 0.997)
But second solution takes long time to solve. thank you
john on 23 Mar 2014
Here: http://www.mathworks.com/matlabcentral/answers/2748-inverse-laplace-problems-matlab-r2010a , they got real result, not complex value. How it is possible?