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Why is my plot not showing?

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Heya :)
Heya :) on 16 Oct 2020
Edited: dpb on 18 Oct 2020
Only axes are appearing but plot is not showing. Please help me to detect the error i am making in the program. Apologies for a long code.
clear all; close all; clc;
test_points=3;
start_point=1000;
x_rec(1)=x(start_point);
x_real(1)=x(start_point);
c1=ksaix(1);
c2=ksaix(2);
c3=ksaix(3);
c4=ksaix(4);
c5=ksaix(5);
c6=ksaix(6);
c7=ksaix(7);
c8=ksaix(8);
c9=ksaix(9);
c10=ksaix(10);
c11=ksaix(11);
c12=ksaix(12);
c13=ksaix(13);
c14=ksaix(14);
c15=ksaix(15);
c16=ksaix(16);
c17=ksaix(17);
c18=ksaix(18);
c19=ksaix(19);
c20=ksaix(20);
c21=ksaix(21);
c22=ksaix(22);
c23=ksaix(23);
c24=ksaix(24);
c25=ksaix(25);
error=0;
DN=0;
for i=4:test_points
x_rec(i)=c1+c2*x_rec(i-1)+c3*x_rec(i-1)^2+c4*x_rec(i-1)^3+c5*x_rec(i-1)^4+c6*x_rec(i-1)^5+c7*x_rec(i-1)^6+c8*x_rec(i-1)^7+c9*x_rec(i-1)^8+c10*x_rec(i-1)^9+c11*x_rec(i-1)^10+c12*x_rec(i-1)^11+c13*x_rec(i-1)^12+c14*x_rec(i-1)^13+c15*x_rec(i-1)^14+c16*x_rec(i-1)^15+c17*x_rec(i-1)^16+c18*x_rec(i-1)^17+c19*x_rec(i-1)^18+c20*x_rec(i-1)^19+c21*x_rec(i-1)^20+c22*x_rec(i-1)^21+c23*x_rec(i-1)^22+c24*x_rec(i-1)^23+c25*x_rec(i-1)^24;
error=error+(x_rec(i)-x_real(i))^2;
DN=DN+x_real(i)^2;
end
Error_x(count)=sqrt(error)/sqrt(DN);
end
figure
hold on
plot (Data,Error_x,'s-r')

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Heya :)
Heya :) on 17 Oct 2020
Thank you!
dpb
dpb on 17 Oct 2020
x_rec(i)=c1+c2*x_rec(i-1) + c3*x_rec(i-1)^2 + c4*x_rec(i-1)^3 + c5*x_rec(i-1)^4 + ...
c6*x_rec(i-1)^5 + c7*x_rec(i-1)^6 + c8*x_rec(i-1)^7 + c9*x_rec(i-1)^8 + ...
c10*x_rec(i-1)^9+c11*x_rec(i-1)^10+c12*x_rec(i-1)^11+c13*x_rec(i-1)^12+ ...
c14*x_rec(i-1)^13+c15*x_rec(i-1)^14+c16*x_rec(i-1)^15+c17*x_rec(i-1)^16+ ...
c18*x_rec(i-1)^17+c19*x_rec(i-1)^18+c20*x_rec(i-1)^19+c21*x_rec(i-1)^20+ ...
c22*x_rec(i-1)^21+c23*x_rec(i-1)^22+c24*x_rec(i-1)^23+c25*x_rec(i-1)^24;
is
x_rec(i)=polyval(flip(ksaix),x_rec(i-1));
NB: polyval is defined as
Y = C(1)*X^N + C(2)*X^(N-1) + ... + C(N)*X + C(N+1)
so must reverse order of coefficient array.
dpb
dpb on 17 Oct 2020
As for the original question, anything that uses a polynomial to the 24th power is just asking for numerical troubles--either over- or underflow and imprecision.
As another said, probably you're ending up with NaN or Inf as results.

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Answers (1)

Image Analyst
Image Analyst on 17 Oct 2020
Look at the first few lines:
clear all; close all; clc;
test_points=3;
start_point=1000;
x_rec(1)=x(start_point);
Now you try to get x(start_point) but you never defined it. SO that throws an error. Or if you did (in another script), you blew it away with the clear all command.

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