How can I Write a code that will allow a vector of positive integers in x, as a user input, to evaluate the equation listed below.For odd numbers we will use the following equation

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John Nowak 2019-9-18

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评论： dpb 2019-9-18

 x= input('\nPlease input a 5 values in vector notation:');
i = 1;
for i = 1:5
  if rem(i,2) ==1; i = 2.*(i.^2) + 8*i - 3;
    if rem(i,2)==0;
        i = 2.*(i.^2) - 8*i + 3;
    end
  end 
  i=i+1
end 
disp(i)

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John Nowak 2019-9-18

在 MATLAB Online 中打开

Sorry the question did not all paste.. the full question is:

How can I Write a code that will allow a vector of positive integers in x, as a user input, to evaluate the equation listed below. For odd numbers we will use the following equation: 2x^2 + 8x - 3

For even numbers we will use the following equation

2x^2 - 8x + 3.

I am stumped

dpb 2019-9-18

See Answer below...

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Answer 1

dpb 2019-9-18

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x= input('\nPlease input a 5 values in vector notation:');
b=nan(size(x));             % initialize to something
isodd=mod(x,2)==1;
y(isodd) =polyval([2  8 -3],x(isodd);   % evaluate  2x.^2 + 8x - 3 for odd x
y(~isodd)=polyval([2 -8  3],x(~isodd);  % evaluate  2x.^2 - 8x + 3 for even x
disp(y)

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John Nowak 2019-9-18

is there anyway you write this code as an if else statement?

thanks!

dpb 2019-9-18

Sure... :)

Just carry on as you began with rough93 pattern incorporating my comments...since it is homework, let's see your continuing work towards a solution rather than just "giving away the store"....will continue to provide hints or answer specific questions other than "just do it"... :)

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Answer 2

rough93 2019-9-18

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It looks like you're using i within your calculations when you should be using x. Assuming your vecor input is [1 2 3 4 5]:

    i = 1;
    for i = 1:5
    if rem(x(1),2) ==1; x = 2.*(x.^2) + 8*x - 3;
        if rem(x,2)==0;
            x = 2.*(x.^2) - 8*x + 3;
        end
    end 
    i=i+1
    end 
    

You may also want to make your second if an ifelse and add an else condition to clean up the code and prevent errors.

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dpb 2019-9-18

编辑：dpb 2019-9-18

The if above for rem(x,2)==0 won't work as it returns a logical vector which will be true only if all elements are true. Need to test x(i) in the loop.

The assignment is also global and overwrites the input x vector in the calculations.

Also incrementing i is automagic in the loop for expression and neither the initialization before the loop nor the incrementing statement are of any use and should be eliminated entirely.

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