# why my matlab didn't plot anything?

1 view (last 30 days)
Edited: DGM on 10 Sep 2021
So i tried to plot a graph using this code, but it won't plot anything. I believe my code is plotting a point but not a line and i don't know why
clear all
m = 85
m = 85
g = 9.81
g = 9.8100
ti = 0
ti = 0
tf1 = 9
tf1 = 9
v(1)= -20
v = -20
h = 1
h = 1
c1 = 11
c1 = 11
dv1 = @(g,c1,v,m) g-c1*v/m
dv1 = function_handle with value:
@(g,c1,v,m)g-c1*v/m
while(ti<tf1)
v = v + dv1(g,c1,v,m)*h
ti = ti+h
plot(ti,v)
drawnow
end
v = -7.6018
ti = 1
v = 3.1920
ti = 2
v = 12.5889
ti = 3
v = 20.7698
ti = 4
v = 27.8919
ti = 5
v = 34.0924
ti = 6
v = 39.4904
ti = 7
v = 44.1899
ti = 8
v = 48.2812
ti = 9

Matt J on 10 Sep 2021
Edited: Matt J on 10 Sep 2021
m = 85;
g = 9.81;
ti = 0;
tf1 = 9 ;
v(1)= -20;
h = 1;
c1 = 11;
dv1 = @(g,c1,v,m) g-c1*v/m;
k=1;
while(ti<tf1)
k=k+1;
v(k) = v(k-1) + dv1(g,c1,v(k-1),m)*h;
ti=ti+h;
plot(0:h:ti,v); drawnow
end

DGM on 10 Sep 2021
Edited: DGM on 10 Sep 2021
m = 85;
g = 9.81;
ti0 = 0;
tf1 = 9;
v0 = -20;
h = 1;
c1 = 11;
dv1 = @(g,c1,v,m) g-c1*v/m;
ti = ti0:h:tf1;
v = zeros(1,numel(ti));
v(1) = v0;
for k = 2:numel(ti)
v(k) = v(k-1) + dv1(g,c1,v(k-1),m)*h;
end
plot(ti,v)
Plotting one point at a time is generally unnecessary and cumbersome. When you plot single points that way with the default linestyle, they are not connected by lines. You could make the dots themselves visible by specifying a marker type other than the default, but storing the results and putting the plot statement outside the loop avoids the hassle and leaves you with vectors that can be used for other things if needed.
It's also generally good to avoid unnecessary while loops, using for-loops when the number of iterations is known beforehand. This avoids any chance of mistakes or unpredicted scenarios that could cause the loop to not terminate. Such an oversight isn't really a big risk with something this small, but it's something to keep in mind as your code gets more complex.

R2021a

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