Error in series summation

Question

Giorgos Papakonstantinou 2013-1-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/59961-error-in-series-summation

评论： REEMA MOHANTY 2020-11-14

I am trying to do a summation of a series as shown below:

syms x n S lf Wf jmpp Rb Wb
Iline=4*jmpp*S*lf/Wf;
I1=(n-1)*Iline*Wf+Iline*x;
I2=n*Iline*Wf;
dR=Rb/Wb;
P1=int(I1^2*dR,0,Wf);
P2=I2^2*dR*S;
Pt=P1+P2;
pb=symsum(Pt,n,1,4);

The summation works fine if I do it for:

pb=symsum(Pt,n,1,6);

or

pb=symsum(Pt,n,1,10);

but for some reason not for 4 and 5!! Do you know why is that?

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Matt J 2013-1-26

Elaborate on "nor for 4 and 5". What do you see and what do you think you should see?

Giorgos Papakonstantinou 2013-1-26

Matt I have elaborated it. Can you see the results? It is strange...

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Answer 1

Giorgos Papakonstantinou 2013-1-26

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https://ww2.mathworks.cn/matlabcentral/answers/59961-error-in-series-summation#answer_72495

在 MATLAB Online 中打开

If I do it for

pb=symsum(Pt,n,1,n);

I get the result:

pb=(8*(2*Rb*S^3*jmpp^2*lf^2*n^3 + 3*Rb*S^3*jmpp^2*lf^2*n^2 + Rb*S^3*jmpp^2*lf^2*n + 2*Rb*Wf*S^2*jmpp^2*lf^2*n^3))/(3*Wb);

I set:

n=4;

I get:

pb =
(1440*Rb*S^3*jmpp^2*lf^2 + 1024*Rb*Wf*S^2*jmpp^2*lf^2)/(3*Wb)

Then I would like to confirm the result by doing the calculations for n=1 until n=4 as shown below:

Pa1=int((Iline*x)^2*dR,0,Wf);
Pa2=(Iline*Wf)^2*dR*S;
Pb1=int((Iline*Wf+Iline*x)^2*dR,0,Wf);
Pb2=(2*Iline*Wf)^2*dR*S;
Pc1=int((2*Iline*Wf+Iline*x)^2*dR,0,Wf);
Pc2=(3*Iline*Wf)^2*dR*S;
Pd1=int((3*Iline*Wf+Iline*x)^2*dR,0,Wf);
Pd2=(4*Iline*Wf)^2*dR*S;
Pt=Pa1+Pa2+Pb1+Pb2+Pc1+Pc2+Pd1+Pd2;

Then I take the fraction

pb/Pt

and I get 1. In this way review that the series is working fine.

But for some reason when I am asking from matlab to do the summation from 1 until 4. I get the following error.

Error using mupadmex
Error in MuPAD command: The number of arguments is incorrect. [has]
    Evaluating: sum
Error in sym/symsum (line 65)
   rSym = mupadmex('symobj::map',f.s,'symobj::symsum',x.s,a.s,b.s);
Error in sumseries (line 17)
pb=symsum(Pt,n,1,4);