Array indices must be positive integers or logical values.

g=9.81;

m=95;

v=25;

t=10;

f(x)=m*g/x*(1-exp(-(x/m)*t));

Array indices must be positive integers or logical values.

I am taking this message. What is wrong at the code?

[Stephen23]

Most likely x is not a positive integer. What is the value of x ?

Are you actually trying to define a function of the independent variable x ?

[Dilsah Bahçeci]

ı am gonna find x by using fzero function. How can ı correct in your opinion?

Answer 1

[Star Strider]

That notation only will work in the Symbolic Math Toolbox. Use Anonymous Functions to create functions for numeric calculations outside the Symbolic Math Toolbox.

Perhaps —

g=9.81;
m=95;
v=25;
t=10;
f = @(x) m*g./x.*(1-exp(-(x/m)*t));

xval = 10;
x = fzero(@(x)f(x)-xval,100)

x = 93.1899

xv = linspace(-1,150);
figure
plot(xv,f(xv),   x, xval,'rs')

The function will not cross the x-axis. It is possible to determine where it will reach a specific value.