# Function & Plot?

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I am trying to solve an example that wants me to solve the equation(c=c-(k*c*t)) and plot the graph between c and t, knowing that t is the step size which in my case is 0.15, and k is constant=0.3, and c=15 initially, I am looking to create a function that calculate the decaying rate with time I have tried the following code: function Decayrate ()

k=0.3;

c=15;

t=(0:0.15:2.1);

c=c-(k*c*t)

plot (t,c)

but the problem is that it when applying the equation the t that going to be used is the the t value and not the step size (0.15), so how can I apply the step size instead of t to the equation, and plot c with t at the same time knowing that at t=0 c=15?

##### 1 Comment

Eng. Fredius Magige
on 17 Oct 2015

### Answers (1)

Martin Schätz
on 17 Oct 2015

From what i did understand, if c=15 initialy, you have to change it every time. so the newc=c-(k*c*t) and also t will change every time. So i thing the code should look like this:

clear all

k=0.3;

c=15;

t=(0:0.15:2.1);

c=zeros(1,15)

Setup initial c to 15

c(1)=15;

for every next c, i will use the previous c and right t

for i=2:15

c(i)=c(i-1)-(k*c(i-1)*t(i))

end

figure

plot(t,c), axis tight

xlabel('t')

ylabel('c')

##### 2 Comments

Steven Lord
on 17 Oct 2015

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