Why won't this function plot?

Question

AUSTIN WHITELEY 2022-1-19

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评论： Steven Lord 2022-1-19

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?

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Steven Lord 2022-1-19

在 MATLAB Online 中打开

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

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Answer 1

Simon Chan 2022-1-19

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No need to use the for loop, Just use the following:

plot(c1_exp)

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AUSTIN WHITELEY 2022-1-19

that doesn't work

Voss 2022-1-19

Are one or more of the constants NaN?

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Answer 2

Voss 2022-1-19

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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))