Display negative results with "i" rather than negative sign

Hello,

I'm fairly new to Matlab and I think the solution to this is something to do with fprintf, but I don't know for sure. My assignment is to write a program to determine the nth root between 2<n<99 and any number between -10,000,000 and 10,000,000. I'm not allowed to use Matlab's SQRT function. For negative numbers they have to be displayed using an i rather than a negative sign (ex. 3i not -3). The instructor never said we couldn't use the nthroot function, but just in case I wrote two sets if code very similar. On the one where I take a number to the fractional power (ex. 81^1/2 =9) all is well until I put in a negative number. Then I get two results. Then on the other program using the nthroot function the answer is displayed as a negative rather than i and I can't figure out how to convert these answers. Here is my code. Can anyone help? Thanks in advance

Program 1:

n=input ('enter a number between -10,000,000 and 10,000,000: ');

if n<-10000000 || n>10000000

disp('error on input number');

pause

exit

end

r=input ('enter the nthroot to be calculated: ');

if r<2 || r>99

disp('error on input number');

pause

exit

end

rr=(1/r);

a=n^rr

Program 2:

n=input ('enter a number between -10,000,000 and 10,000,000: ');

if n<-10000000 || n>10000000

disp('error on input number');

pause

exit

end

r=input ('enter the nth root to be calculated: ');

if r<2 || r>99

disp('error on input number');

pause

exit

end

a=nthroot(n,r)

Answer 1

[KALYAN ACHARJYA]

Is this: First one, if OK, do the same for 2nd program

n=input ('enter a number between -10,000,000 and 10,000,000: ');
if n<-10000000 || n>10000000
    disp('error on input number');
else
    r=input ('enter the nthroot to be calculated: ');
    if r<2 || r>99
    disp('error on input number nthroot');
    else
    rr=(1/r);
    a=n^rr
    end
end

[Leanne Dozier]

If I run that code and I put in 27 for n and 3 for r, I get an answer of 3 which is correct. Then if I put in -27 for n and 3 for r I get two different answers (1.5000+2.5981i). I only want to get one answer. The correct answer is -3. I looked this up (displaying two answers) and it is correct according to matlab, but I don't understand why. ;)

When I run the second code with the nthroot function and I input -27 as the number and 3 as the nthroot I get -3 as the answer, which is correct, but I need it to display 3i rather than -3 and I can't figure out how to convert it.

I only need one of these programs. I just tried it two different ways to see if I could figure it out on my own.

[KALYAN ACHARJYA]

Please do read here about roots of negative number, I just forced the code to do as per your expectation. But Maths is always pure, please do read.

n=input ('Enter a number between -10,000,000 and 10,000,000: ');
if n<-10000000 || n>10000000
    disp('error on input number');
else
    r=input ('Enter the nthroot to be calculated: ');
    if r<2 || r>99
    disp('Error on input number');
    else
    a=-double(n<0)*abs(n)^(1/r)+double(n>0)*(n)^(1/r)
    end
end

[Leanne Dozier]

I ran your code just now and yes it displays the correct answer (ex. cube root of -27= -3) which is correct, but is there a way to make it display "3i" instead of "-3" like it's doing?

Thank you for your efforts!

[KALYAN ACHARJYA]

Watever you want you can display, is this?

a=double(n<0)*abs(n)^(1/r)*i+double(n>0)*(n)^(1/r)

use

format shortG 

at the beginning of the code to avoid extra decimal3.0000i points

[Leanne Dozier]

That one is much better! Thank you so much!! It's been driving me crazy for hours! I appreciate it!

[KALYAN ACHARJYA]

It's my pleasure @Leanne Dozier