How do i get an equation in an exponent

I have this equation

I = 25e(-R/L)*t

I have inputs for R,L, and t but it gives me an error just the same.

R= [1 2 3 5]
L = input('blah blah','s')
t = linspace(0,2,20)
I=25exp((-R/L*t))

floating point error

OR

Equ_1 = (-R/L)*t
I=25exp(Equ_1) 

invalid use of operator.

[Walter Roberson]

MATLAB has absolutely no implied multiplication.

[Brendan Proaps]

What does that mean, I barely know anything about programming.

[Walter Roberson]

Implied multiplication is when you place two items (numbers or expressions) beside each other without any operator between them, and you expect that they will be multiplied. For example, would almost certainly be intended to mean 25 multiplied by R, , but MATLAB will never interpret 25R or 25 R as multiplication. You need to put in explicit multiplication symbols, 25.*R

Answer 1

[Walter Roberson]

R= [1 2 3 5];
L = input('blah blah ');    %NOT 's'
t = linspace(0,2,20);

[Rg, Lg, tG] = ndgrid(R, L, t);
I = 25 .* exp((-R./L.*t));

The result will be 4 by numel(L) by 20