Solving equations using MATLAB

Question

I got an online question which I couldn’t understand.

The question is:

Create a script to ask the user to create a random number using the following equation :

1. Plot x(t) with customize the figure yellow and red color and dash line.
2. Solve the equation with symbolic and differentiate it.

I tried to solve it as following:

clc; clear all; 

syms x;
Xt = int(100*rand*sin(x),-100,100); 
plot(Xt);   % The first question 
Y = solve(100*rand*sin(x)); 
Y2 = diff(Xt,x);

The problem I face is that Xt, Y and Y2 are all zeros. Did I understand the question right? How to solve it?

Answer 1

Possibly, could plot the functions with respect to x. Kinda concerned since the function is called X(t) though. Seems like it should be changing with respect to t or some kind of time variable. The colour and line properties can be configured by adding the short-hand for the colour followed by the line type in this case I used a dashed red line denoted as r-- in the fplot() line. In this example, I also used hold on to add a yellow underline. If you need the figure background colour to be yellow add set(gcf,'color','y'); to configure the current figure, gcf. Not quite sure which portions or plots need the yellow colour. To plot symbolic functions using the fplot() function can be a useful method. This function can optionally take a second argument that is an array describing the horizontal/x-axis bounds/range to plot the function for. Also note that rand will only evaluate to doubles in the range from 0 to 1.

clear;
clc; 
clf;

syms x;

Xt = int(100*rand*sin(x)); 
Lower_Bound = -100;
Upper_Bound = 100;

subplot(2,1,1); fplot(Xt,[Lower_Bound Upper_Bound],'y');  
hold on
subplot(2,1,1); fplot(Xt,[Lower_Bound Upper_Bound],'r--'); 
title("Plot of X(t)");
xlabel("x"); ylabel("Amplitude");
hold off

Solution = int(100*rand*sin(x),Lower_Bound,Upper_Bound); 
Solution

Y2 = diff(Xt,x);

subplot(2,1,2); fplot(Y2,[Lower_Bound Upper_Bound])
title("Differentiation of X(t) -> Y(t)");
xlabel("x"); ylabel("Amplitude");

Ran using MATLAB R2019b