Is it my equation wrong? Cause I get a weird graph for this equation.

clear; clc;
syms t; 
f=exp(-2*t)*tanh(4*t); 
c=0.000009; 
I=c*diff(f);
figure(1); fplot(I); grid; xlabel('time'); ylabel('current'); title('current vs time');

Answer 1

[Voss]

If the current is given by that function of time i(t), and you should plot the current vs time, then there is no need to do c*diff(f) (not for part A anyway).

Also, specify a time interval in fplot that starts at 0.

syms t; I=exp(-2*t)*tanh(4*t); %c=0.000009; I=c*diff(f);
figure(1); fplot(I,[0 5]); grid; xlabel('time'); ylabel('current'); title('current vs time');

Answer 2

[Sam Chak]

Hi @Muhammad Harriz Bin Zamri

Missing dot.

t = 0:0.01:5;
x = exp(-2*t).*tanh(4*t);
plot(t, x, 'linewidth', 1.5)
xlabel('t')
ylabel('i(t)')
grid on

Answer 3

[Image Analyst]

You may need to specify a time vector rather than use syms. Like

t = linspace(0, 5, 500);
f=exp(-2*t).*tanh(4*t); 
c=0.000009; 
I=c*diff(f);
figure(1); 
plot(t(2:end), I, 'b-', 'LineWidth', 2); 
grid; 
xlabel('time'); 
ylabel('current'); 
title('current vs time');