how do i write a function that take a vector and only displayes prime elements

I have a homework where i have to write a function that takes in a vector x and outputs a vector p that only has prime elements

This is what i managed to do so far:

tf=isprime([4 3 6 7 1 2 4 6 8 9]) tf = 1×10 logical array

   0   1   0   1   0   1   0   0   0   0
Im kinda new to matlab

Answer 1

[Rik]

You are very close. The only thing you need to do is use the logical vector to keep only prime elements. BTW, are you sure you are allowed to use the isprime function for your homework assignment?

x=[4 3 6 7 1 2 4 6 8 9];
tf=isprime(x);
x_output=x(tf);

A helpful resource to learn using Matlab is available here.

[Ahmad al-falahi]

yeah thanks i did this x=[91 39 87 51 89 37 65 29 41 43 97]

t=isprime(x)

p=t.*x

but its not a program, i think i will use your ways and see what happens XD

[Ahmad al-falahi]

yeah this is better, now the zeroes are gone, thanks

[Ahmad al-falahi]

Oh no, sorry they want us to Use the "if, if-elseif, for and while commands

[Rik]

Well, then it's time to read the documentation for the while function, if and elseif. Just type

doc while

in your command window to open the documentation viewer.

Use a for or a while loop to loop through all elements of the input vector (hint: start from the back of your vector). Then use conditional statements to remove elements that are not prime.

I don't know a way to give you better hints without making your homework for you.

[Ahmad al-falahi]

thanks for the help man.

Answer 2

[KSSV]

A = [4 3 6 7 1 2 4 6 8 9] ;
idx=isprime(A)
iwant = A(idx)

Read about MATLAB logical indexing.

[Ahmad al-falahi]

thanks

[Ahmad al-falahi]

Oh no, sorry they want us to Use the "if, if-elseif, for and while commands. do you know how to do that ?