# How can I simplify my expression?

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Bálint Nagy il 5 Mag 2019
Risposto: gonzalo Mier il 6 Mag 2019
Hey Guys!
So I'm in the middle of a modelling assignment, and have to perform an inverse-laplace transformation on the following expression:
(4.1567898247199520341942099474821e+54*Ua)/(s*(100229224846904105411357376442422.0*s^6 + 5.9483485126126760990974540409349e+35*s^5 + 5.0239631343165245308229429056249e+40*s^4 + 2.9725399793555455758222675933522e+44*s^3 + 1.0212281680153877722127895364433e+48*s^2 + 5.6753104089399036705416819827312e+51*s + 1.0269914923230344802781707591666e+54))
My problem is that this returns a sum of exponential functions containing complex numbers, as below
4.0475406620140304336968591117778*Ua + 0.048633477607650367346402317141675*Ua*exp(-5720.286485024099496269401688463*t) - 4.1776273848702626395266209427561*Ua*exp(-186.91307534353595311970441088345*t) - Ua*exp(t*(- 1.3058525120961962405107425874867 - 21910.096393659412026550844582755i))*(0.00018263285547812810287333894168844 - 0.000049523771938216719441312262428056i) - Ua*exp(t*(- 1.3058525120961962405107425874867 + 21910.096393659412026550844582755i))*(0.00018263285547812810287333894168844 + 0.000049523771938216719441312262428056i) + Ua*exp(t*(- 12.466668994798763511731927336948 - 4467.9831446674244095221560260197i))*(0.040909255479769047344553095860047 - 0.056379618619562305355740635447079i) + Ua*exp(t*(- 12.466668994798763511731927336948 + 4467.9831446674244095221560260197i))*(0.040909255479769047344553095860047 + 0.056379618619562305355740635447079i)
Now, as you can see, the parts that have complexes in it are complex conjugates and therefore the imaginary parts could be eliminated - meaning that this expression simplifies into a real expression. My problem is that I just can't get matlab into doing this simplification.
What I have tried so far:
rewrite('sincos'), simplify('Criterion','preferReal'), but I still couldn't eliminate the imaginary parts.
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Bálint Nagy il 5 Mag 2019
unfortunately not.
Star Strider il 5 Mag 2019
This may be a bug. It would definitely be an enhancement request.
If you want to report it as such, use the Contact Us telephone handset icon in the upper right of this page. (Have MATLAB open at the time so you can execute the ver command.)

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### Risposta accettata

gonzalo Mier il 6 Mag 2019
It only needs more time to simplify:
I'm doing:
simplify(4.0475406620140304336968591117778*Ua + 0.048633477607650367346402317141675*Ua*exp(-5720.286485024099496269401688463*t) - 4.1776273848702626395266209427561*Ua*exp(-186.91307534353595311970441088345*t) - Ua*exp(t*(- 1.3058525120961962405107425874867 - 21910.096393659412026550844582755i))*(0.00018263285547812810287333894168844 - 0.000049523771938216719441312262428056i) - Ua*exp(t*(- 1.3058525120961962405107425874867 + 21910.096393659412026550844582755i))*(0.00018263285547812810287333894168844 + 0.000049523771938216719441312262428056i) + Ua*exp(t*(- 12.466668994798763511731927336948 - 4467.9831446674244095221560260197i))*(0.040909255479769047344553095860047 - 0.056379618619562305355740635447079i) + Ua*exp(t*(- 12.466668994798763511731927336948 + 4467.9831446674244095221560260197i))*(0.040909255479769047344553095860047 + 0.056379618619562305355740635447079i),1000)
And the imaginary part is not there anymore.
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