How to find a Y value of a given X?

Hello, this is a very simple question. I am writing an equation for v given t:

t = 0:0.00001:0.01;
v= 50*exp(-1600*t) - 50*exp(-400*t);

How would I find the value of v at a certain t? I want to find what v is when t=0.000625.

Answer 1

[Star Strider]

This is easiest if you create ‘v’ as an anonymous function:

t = 0:0.00001:0.01;
v = @(t) 50*exp(-1600*t) - 50*exp(-400*t);

ti = 0.000625;
Out = v(ti)

figure
plot(t, v(t))
hold on
plot(ti, v(ti), 'r+')
hold off
grid

See Anonymous Functions for details.

[Rishab Vadvadgi]

Thank you! One more question: can I use functions I have written to create a new one? For example, I am trying to multiply a function v and a function i together to make a new function p.

v = @(t) 50*exp(-1600*t) - 50*exp(-400*t);
i = @(t) (5*exp(-1600*t) - 5*exp(-400*t)) * 0.001;
p = @(t) v*i;

However, this gives me an error. What is the proper way to do this?

[Rishab Vadvadgi]

Thanks! I ended up figuring out right after I posted haha

[Star Strider]

My pleasure!

To calculate with functions, it is necessary to evaluate them to do the calculation:

p = @(t) v(t).*i(t);

That works. Note also the use of element-wise multiplication, .* instead of * .

Example —

figure
plot(t, p(t))
grid

.

Answer 2

[Johannes Fischer]

You want to use an anonymous function.

So in your case:

% define the anonymous function
v = @(t) 50*exp(-1600*t) - 50*exp(-400*t);

% call it
v(0.000625)

[Rishab Vadvadgi]

Thank you! One more question: can I use functions I have written to create a new one? For example, I am trying to multiply a function v and a function i together to make a new function p.

v = @(t) 50*exp(-1600*t) - 50*exp(-400*t);
i = @(t) (5*exp(-1600*t) - 5*exp(-400*t)) * 0.001;
p = @(t) v*i;

However, this gives me an error. What is the proper way to do this?

Answer 3

[BOB MATHEW SYJI]

Hope this helps. x is the input and sol is the value of v at x (in this case x=0.000625)

syms v(t)
x=0.000625;
v(t)= 50*exp(-1600*t) - 50*exp(-400*t);
sol=double(v(x));