MATLAB Answers

my program not work

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ebi
ebi on 19 Oct 2013
Commented: ebi on 20 Oct 2013
hello my program not work , i want to form F and then according to formula, calculate fourier coefficient and fourier series of F and plot them . n=boundary of sigma, w1=is frequence .
clc
clear
L=input(' define L (lenght of wagon -m) : ');
V=input(' define V (speed of train -km/h) : ');
X1=input(' define X1(distance betwean 2 wagon -m) : ');
X2=input(' define X2(distance betwean 2 middle wheels -m): ');
X=input(' define X (distance betwean 2 near wheels -m) : ');
W=input(' define W (total weight of wagon and passenger -ton) : ');
disp( ' ' )
disp('Please wait 5 seconds only!');pause(1);
disp('Press any key to see All input.'); pause;
disp( ' ' )
V=V*1000/3600;disp([' *** V : (speed of train)= ',num2str(V),' m/s'])
disp([' *** L : (lenght of wagon) = ',num2str(L),' m'])
disp([' *** X1: (distance betwean 2 wagon) = ',num2str(X1),' m'])
disp([' *** X2: (distance betwean 2 middle wheels) = ',num2str(X2),' m'])
disp([' *** X : (distance betwean 2 near wheels) = ',num2str(X),' m'])
disp([' *** W : (total weight of wagon) = ',num2str(W),' ton'])
F1=W*9.81/8;
disp([' *** F1: (force of 1 wheel) = ',num2str(F1),' kN'])
t1=X/V;t2=(X+X2)/V;t3=(2*X+X2)/V;t4=(2*X+X2+(L-X2-2*X)+X1)/V;
disp([' *** F1 = ',num2str(F1),' kN'])
disp([' * t1 = ',num2str(t1),' s'])
disp([' * t2 = ',num2str(t2),' s'])
disp([' * t3 = ',num2str(t3),' s'])
disp([' * t4 = ',num2str(t4),' s'])
%t1 =0.0001*round(10000*t1);
%t2 =0.0001*round(10000*t2);
%t3 =0.0001*round(10000*t3);
%t4 =0.0001*round(10000*t4);
%F1 =0.0001*round(10000*F1);
s=input(' define s (number of sampeling > 500 ) : ');
t = 0:1/s:t4;
F = zeros(size(t));
F((t>=0&t<=t1)) = F1;
F((t>t1&t<t2)) = 0;
F((t>=t2&t<=t3)) = F1;
F((t>=t3&t<=t4)) = 0;
T=t4;
w1=2*pi/T;
a0=(1/T)*F*((t1-0)+(t3-t2)); % fourier coefficient
n=[0:1:input(' define n (sigma boundary) > 50 ) : ')];
an=2/T*F/(w1*n)*(sin(w1*n*t1)-0+sin(w1*n*t3)-sin(w1*n*t2)); % fourier coefficient
bn=2/T*F/(w1*n)*(-cos(w1*n*t1)+0-cos(w1*n*t3)+cos(w1*n*t2)); % fourier coefficient
subplot(4,1,1)
plot(t,F)
subplot(4,1,2)
plot(an),grid on
f=a0+an*cos(w1*n.*t/T)+bn*sin(w1*n.*t/T); %fourier Series
subplot(4,1,3)
plot(n,f),grid on

  1 Comment

Yannick
Yannick on 19 Oct 2013
What exactly doesn't work in your program? What error or warning message do you get?

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Answers (1)

Yannick
Yannick on 19 Oct 2013
Edited: Yannick on 19 Oct 2013
One problem is that you define n as a vector of values. When you then plug it into an and bn, it is trying to do matrix multiplications and "divisions" between vector -- something that is not possible in general (unless the sizes match up correctly), and anyway not what you want here (if you have 60 n values, it looks like you are expecting 60 an and 60 bn values).
So instead of * and /, you want to use the element-wise operators .* and ./. For more info: Array vs. Matrix Operations.

  2 Comments

ebi
ebi on 20 Oct 2013
i try to correct my mistake about sizes of matrix an , bn , f , t
and then plot fourier form of f . but i think my plot shape is not true
it must be like pictures that is attached.
my plot
true plot
t1=X/V;t2=(X+X2)/V;t3=(2*X+X2)/V;t4=(2*X+X2+(L-X2-2*X)+X1)/V;
disp([' *** F1 = ',num2str(F1),' kN'])
disp([' * t1 = ',num2str(t1),' s'])
disp([' * t2 = ',num2str(t2),' s'])
disp([' * t3 = ',num2str(t3),' s'])
disp([' * t4 = ',num2str(t4),' s'])
%t1 =0.0001*round(10000*t1);
%t2 =0.0001*round(10000*t2);
%t3 =0.0001*round(10000*t3);
%t4 =0.0001*round(10000*t4);
%F1 =0.0001*round(10000*F1);
t =[0:0.001:t4];
F = zeros(size(t));
F((t>=0&t<=t1)) = F1;
F((t>t1&t<t2)) = 0;
F((t>=t2&t<=t3)) = F1;
F((t>=t3&t<=t4)) = 0;
subplot(4,1,1)
plot(t,F),grid on
T=t4;
w1=2*pi/T;
a0=(1/T)*F1*((t1-0)+(t3-t2));
n=input(' define n (sigma boundary) > 350 ) : ');
an=[1:1:n];
bn=[1:1:n];
f=[1:1:n];
t=linspace(0,t4,n);
for i=1:n
an(1,i)=2/T*F1/(w1*i)*(sin(w1*i*t1)-0+sin(w1*i*t3)-sin(w1*i*t2));
bn(1,i)=2/T*F1/(w1*i)*(-cos(w1*i*t1)+0-cos(w1*i*t3)+cos(w1*i*t2));
f(1,i)=a0+an(1,i)*cos(w1*i*t(1,i)/T)+bn(1,i)*sin(w1*i*t(1,i)/T); %fourier serie
end
subplot(4,1,2)
plot(an),grid on
subplot(4,1,3)
plot(bn),grid on
subplot(4,1,4)
plot(f),grid on
ebi
ebi on 20 Oct 2013
i just want to write a program to get the data from user and form formula of the piecewise force-time function and then plot it ,then plot fourier view of them and transform fourier and force spectrum .
please tell me the best way for define them.

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