# Why won't this function plot?

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AUSTIN WHITELEY on 19 Jan 2022
Commented: Steven Lord on 19 Jan 2022
For some reason I can't plot this function.
t=0:30;
c1_exp = b1*exp(-a1*t) + b2*exp(-a2*t);
All variables except for t are constants.
I've tried
fplot(c1_exp, 'g-', 'Linewidth', 3)
and
for ii= 1:30
plot(c1_exp(:,ii))
end
Nothing happens but I don't get any error messages.
What am I doing wrong?
Steven Lord on 19 Jan 2022
What are the magnitudes (or the actual values) of your coefficients? If the value inside the exp calls gets too small, the exponential would underflow to 0.
exp(-750) % underflow
ans = 0
So if your a values were on the order of say 1000 only the points with t = 0 could possibly plot.
a = 1000;
t = 0:10;
y = exp(-a*t)
y = 1×11
1 0 0 0 0 0 0 0 0 0 0

Simon Chan on 19 Jan 2022
No need to use the for loop, Just use the following:
plot(c1_exp)
##### 2 CommentsShowHide 1 older comment
_ on 19 Jan 2022
Are one or more of the constants NaN?

_ on 19 Jan 2022
Try
plot(c1_exp)
or
plot(t,c1_exp)
With your for loop, you're plotting one data point at a time, which is impossible to see without a data marker. And fplot() is for plotting with a function handle, e.g.,
fplot(@(t) b1*exp(-a1*t) + b2*exp(-a2*t))

R2021a

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