USer Defined Function problem

Write a user-defined MATLAB function named PBTask4p1_f.m for the following math function with x the input argument and y the output: ?(?) = 3.2? 4 − 5? 2 − 7? The function should work for x being a scalar or a vector.

Use the function to calculate y(-5) and y(4) and display the results in command window b) Use the function to make a plot of the function y(x) for -5 ≤ x ≤ 5. Label the x-axis and y-axis of the plot like the one as follows.

I am new at Matlab ,Any help would be appriciated.Thank you

[Ameer Hamza]

Since you are new to MATLAB, this introduction to MATLAB functions will get you started: https://www.mathworks.com/help/matlab/ref/function.html

[A M Saif Ben Kabir Amit]

I figure out thr code seems like these.but it doesn't work

function [w,z]=PBTask4p1(x)
w=3.2*x^4-5*x^2-7^x
end

[Ameer Hamza]

What does not work? What is the error? Also, you function only need output 'w', why have you put 'z' in the output arguments.

[A M Saif Ben Kabir Amit]

function w=PBTask4p1(x)
w=3.2*x^4-5*x^2-7^x
end

PBTask4p1_f(-5)
w =1.8750e+03
ans =1.8750e+03
>> PBTask4p1_f(4)
w =-1.6618e+03
ans =-1.6618e+03

I got these output after removing the z from output.

Now how can I plotfrom this instruction (Use the function to make a plot of the function y(x) for -5 ≤ x ≤ 5.)

Thank You

>>

Answer 1

[Ameer Hamza]

Since you have already written the function, let me give you some information. In MATLAB '*' is used to indicate matrix multiplication. To do scalar multiplication, change the '*' operator in your code to '.*'. Like this

function w=PBTask4p1(x)
    w = 3.2.*x.^4 - 5.*x.^2 - 7.^x;
end

Then create a vector of x values. Some thing like this

x = -5:0.1:5;

The use this x as input to PBTask4p1 and save the output in a variable. And then you can use plot() function

plot(x,w)

to create a plot.

[A M Saif Ben Kabir Amit]

May I Need to write all the code in function scrip or something in command window?

[Ameer Hamza]

This need to be saved in PBTask4p1.m

function w=PBTask4p1(x)
    w = 3.2.*x.^4 - 5.*x.^2 - 7.^x;
end

and you can run the rest of code in command window.

[A M Saif Ben Kabir Amit]

Ok I got it now.Thank You for your kind help.

[Ameer Hamza]

I am glad to be of help.