Plot always appears as a straight line
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Hieu Nguyen
le 4 Déc 2017
Commenté : Roger Stafford
le 5 Déc 2017
v = [0:100];
m = 4.65*10.^-26;
y = ((m*v)/(4.14*10.^-21)).*exp((-m*v.^2)/2*4.14*10.^-21);
plot(v,y)
title('Density fucntion at t1 and t2')
Hi, I don't know how to fix this but my graph appears to be a straight line intead of an exponential curve. Thanks a lot!
1 commentaire
Roger Stafford
le 5 Déc 2017
@Hieu. Here's a demonstration of why you should be careful with how you use parentheses:
x = 60/5*12
y = 60/(5*12)
z = 60/5/12
Notice that in 'y' and 'z' there is division by 12, whereas in 'x' it is multiplied. That is apparently the source of your difficulty with the quantity 4.14*10.^-21. It was multiplied rather than divided because you left out the all-important parentheses.
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Roger Stafford
le 4 Déc 2017
Are you sure the second "4.14*10.^-21" doesn't belong in the denominator:
y = ((m*v)/(4.14*10.^-21)).*exp((-m*v.^2)/(2*4.14*10.^-21));
If so, and if you change the range of v to:
v = [0:1000];
you will get a nicely curved plot.
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Greg
le 4 Déc 2017
First, I suspect you missed parenthesis is your exp denominator. The magic of using constants. Second, most functions look like straight lines if you stay near the origin. Try plotting further out in v.
v = 0:1000;
m = 4.65*10.^-26;
denom = (4.14*10.^-21);
y = ((m*v)/denom).*exp((-m*v.^2)/(2*denom));
a = axes(figure);
plot(a,v,y);
title('Density function at t1 and t2')
2 commentaires
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