how to write a function in interval?

hi,

can you please help me to write this function code in matlab?

thank you in advance

[José-Luis]

What have you tried so far?

I would recommend you to read the "Getting started" part of the documentation.

You might want to look at the fzero() function.

 doc fzero
 doc plot
 doc fplot

[lina]

I attached the question in jpg form can't write the code :'(

Answer 1

[Matt Tearle]

MATLAB Academy can help you learn the basics of MATLAB. Also the Getting Started section of the doc, as Jose-Luis suggested.

For this specific question, you'll need to:

1. create a vector of x values from -2 to 5.
2. create a corresponding vector of y values by evaluating the function.
3. plot y as a function of x.
4. maybe pretty up the graph a bit.

For 2 you'll need to know about array operations. For 4 you can use xlabel, ylabel, title, xlim, ylim, and/or axis.

As Jose-Luis mentioned, if you need the roots exactly, you can use fzero, but that seems a bit advanced for HW#1. Because the function is a polynomial, you could also use polyval (for part 2) and roots. But, again, that seems more than is necessary.

[lina]

thank you Matt it works, but why i get error in mpower ? this is what I start with

 X=[-2:5]
x=X'
the_function =((x^4)-(5.*x^3)+(2.*x^2)+(6.*x)-(4));

[Matt Tearle]

Array operations! You've done 5.*x, which is fine, but actually not needed because 5 is a scalar (so 5*x is the same as 5.*x). However, x is a vector, which means x^2 = x*x is a problem. That exponentiation is interpreted in a matrix sense, so that's where you need your array operator ( .* or .^).

[And because I can't help myself, the square brackets around -2:5 aren't necessary. The brackets are for concatenating values into an array, but the : already makes an array. x = (-2:5)'; will get you the vector a little quicker and cleaner.]

[lina]

Thank u very much u r awesome! It works

[lina]

pardon Matt but there is another problem in plotting dimension

 x=(-2:5);
y=x.^4-5.*(x.^3)+2.*(x.^2)+6.*(x)-4;
plot(y,[-2,5]);

I get this error ??? Error using ==> plot Vectors must be the same lengths.

what should I do?

thank u in advance

[Matt Tearle]

You don't need to specify the domain to the plot function, just the x values and their corresponding y values (in that order): plot(x,y)

If you want to adjust the axis limits that MATLAB chooses, use the xlim and/or ylim functions (use the doc to see how they work).

Answer 2

[Rupa Kupireddy]