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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 
3 个评论
"...however when i try to plot... the curve comes out like this"
You are plotting lots of zeros (to within floating point precision), because that is exactly what you calculated.
"how do i fix this i dont know what i am doing wrong?"
You need to consider the B factor. Note that for a B which is an integer multiple of 2*pi (and you defined B as 4*pi, which is clearly a multiple of 2*pi), the following identity holds true:
sin(B*X) = -sin(B*(1-X))
For example:
B = 2*pi;
X = rand(1,9);
sin(B*X)
sin(B*(1-X))
That is why you are plotting zeros (or at least values very very very close to zero).
Original question by Tyler Daines retrieved from Google Cache (unfortunately their deleted comments are not included):
Trying to plot a sine+sine function but not getting a smooth curve
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
2021-6-29
(Answers Dev) Restored edit
回答（2 个）
DGM
2021-5-11
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'.
RAHUL MAURYA
2021-5-12
0 个投票
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.
1 个评论
RAHUL MAURYA
2021-5-12
Convert B and L in degree from Radian
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