error with graphing exp function

in my code I tried having e to some negative power and graph it but it's not working, any help?

r = 0.5; l=4;
%%given: A(1) and A(2) are two numbers from a vector, and r(1) and r(2) are two other numbers from another vector
vct = A(1)*exp(r(2)*x)+ A(2)*exp(r(1)*x);
x = 0:2:20
figure
expfunc = exp(-x*r/l) %%I want e^(-x*r/l) for that part
plot(x,vct/0.5*(1-expfunc)) %%overall equation should be: vct/0.5*(1-e^(-x*r/l))

[madhan ravi]

r, l ?

[James Tursa]

If x is a vector and r is a vector, what do you expect from the expression -x*r/l?

[seldiora]

oh no, x isn't a vector, it's a variable, r and l are set in the beginning

[James Tursa]

This line makes x a vector:

>> x = 0:2:20
x =
     0     2     4     6     8    10    12    14    16    18    20

Then you have text that says r is a two element vector since you use r(1) and r(2). But your code has r as a scalar. So which is it?

[seldiora]

ah, I re-set r into a vector. So how would I fix this? Graphing vct itself didn't cause any problems.

edit: oh, r isn't meant to be a vector. I solved that but that wasn't the entire problem

[James Tursa]

I could fix your code so it didn't generate errors, but it might not be correct for the problem you are trying to solve. Can you give us the actual wording of the assignment?

[seldiora]

so, I want to graph the current for an inductor. [http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/indt.png] However since the voltage (vct) varies with time, I want to use vct/r*... [the rest is in the image]