# matlab words no help needed

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Tyler Daines on 11 May 2021
Edited: Rena Berman on 29 Jun 2021 at 15:18
I need to plot the sum of 2 sine curves. I can successfully plot (x,y1) and plot(x,y2), they are smooth curves, however when i try to plot(x,y) where y = y1+y2 the curve comes out like this? how do i fix this i dont know what i am doing wrong? Thanks
Rena Berman on 29 Jun 2021 at 15:18

(Answers Dev) Restored edit

DGM on 11 May 2021
What you're looking at isn't meaningful. It's all just rounding error. You're essentially doing this:
y = sin(x) - sin(x);
I'm guessing there's some phase component that's not defined right yet, but I can't really guess at what you need it to be.
f = 2;
A = 1;
v = 1;
L = 1;
l = v/f;
B = (2*pi)/l;
w = 2*pi*f;
t = 0;
x = 0:0.0001:L;
z1 = A*sin(B*x - w*t);
z2 = A*sin(B*(L-x) - w*t);
y = z1+z2;
plot(x,z2); hold on
plot(x,z1);
For the future, please just paste your code using the code formatting tools. I had to retype all that and deal with the sub-pixel ambiguity differentiating the character '1' and 'l'.
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DGM on 11 May 2021
No worries. It was short enough.

VBBV on 11 May 2021
Edited: VBBV on 11 May 2021
%if true
f = 2
f = 2
V = 1; A= 1; L = 1;
LL = V/f
LL = 0.5000
B = 2*pi/LL
B = 12.5664
t = 0; W = 2*pi*f
W = 12.5664
x = 0:0.0001:L;
z1 = A*sin(B*x-W*t)
z1 = 1×10001
0 0.0013 0.0025 0.0038 0.0050 0.0063 0.0075 0.0088 0.0101 0.0113 0.0126 0.0138 0.0151 0.0163 0.0176 0.0188 0.0201 0.0214 0.0226 0.0239 0.0251 0.0264 0.0276 0.0289 0.0302 0.0314 0.0327 0.0339 0.0352 0.0364
z2 = A*sin(B*(L-x)-W*t);
z = z1-z2
z = 1×10001
0.0000 0.0025 0.0050 0.0075 0.0101 0.0126 0.0151 0.0176 0.0201 0.0226 0.0251 0.0276 0.0302 0.0327 0.0352 0.0377 0.0402 0.0427 0.0452 0.0477 0.0503 0.0528 0.0553 0.0578 0.0603 0.0628 0.0653 0.0678 0.0704 0.0729
plot(x,z)
Use z1-z2 instead for smooth curve
Stephen Cobeldick on 13 May 2021
"Does this mean that there is no way to plot y = ysrc + yref?"
I am not sure why you have reached that conclusion.
"I do see why my plot is meaningless."
The plot itself is not meaningless: you have correctly plotted lots of tiny values, because that is what you told MATLAB to plot. The values are numeric noise resulting from operations which are basically equivalent to X+(-X). MATLAB has correctly plotted that numeric noise (because it was all your numeric values are).
Important question: What do you expect to be plotted for X+(-X) ?
Perhaps you could scale the Y limits to suitable values then the numeric noise would not be noticeable at all.

RAHUL MAURYA on 12 May 2021
clear all;
clc;
f = 2;
A = 1;
v = 1;
L = 1*(180/(pi));
l = v/f;
B = ((2*pi)/l)*(180/pi);
w = 2*pi*f;
t = 0;
x=0:0.0001:L;
z1 = (A*sind(B*x - w*t));
z2 = A*sind(B*(L-x) - w*t);
y=(z1+z2);
subplot(3,1,1);
plot(x,z1)
title('X,Z1')
axis([0 10 -1 1])
subplot(3,1,2);
plot(x,z2)
title('X,Z2')
axis([0 10 -1 1])
subplot(3,1,3);
plot(x,y)
title('X,Z1+Z2')
axis([0 10 -2 2])
Convert B and L in radian to degree.
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RAHUL MAURYA on 12 May 2021
Convert B and L in degree from Radian