Help with matlab homework

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Nguyen 2015-2-3

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评论： Youssef Khmou 2015-2-3

The graph of the function , f(x)=a*x^4+b*x^3+c*x^2+d*x+e, passes through the points (-3, 6.8), (-1.5, 15.2), (0.5, 14.5), (2, -21.2), and (5, 10). Write a script that will prompt for the ordered pairs as inputs and solve five equations with the five unknown constants: a, b, c, d, and e. You need to set up a matrix equation and solve for the unknowns by first finding the inverse of a matrix. Solve the system: y = X * h, for h

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John D'Errico 2015-2-3

I fixed the code formatting. When you include code, select it, then click on the button that says "{} code". This will make your code readable for others.

Ok. so you have at least made some effort. Admittedly, it is rarely a good thing to have an interface with lots of input statements. And naming a list of variables as you have will get you in trouble one day. So, how about this as a simplification?

for ind = 1:5
  xy(ind,:) = input('Enter an ordered pair as a vector [a,b]:');
end

This will create an array of size 5x2, where the first column is x, the second column y. You could split the columns apart, perhaps as

x = xy(:,1);
y = xy(:,2);

As for how to create the X matrix, you should look at the vander function. What would vander(x) do then? TRY IT!

If you cannot use vander (read, are not allowed) then ask again, but first, think about what vander produces. Is there a way to create that matrix yourself?

Nguyen 2015-2-3

What is vander? I cannot find it in my book and my professor has not talked about it.

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回答（1 个）

Youssef Khmou 2015-2-3

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编辑：Youssef Khmou 2015-2-3

Since this is homework, partial answer is given, You have to start with the following :

     X=[(-3)^4     (3)^3       (3)^2      3      1;
       (-1.5)^4   (-1.5)^3    (-1.5)^2   (-1.5) 1;
       (0.5)^4    (0.5)^3     (0.5)^2    (0.5)  1;
       (2)^4      (2)^3       (2)^2      2      1;
       (5)^4      (5)^3       (5)^2      5      1];

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Nguyen 2015-2-3

Okay, so I can just type this in to a script? And in the input line of the command box I can just type in the name if the script file and it would give me an answer?

Youssef Khmou 2015-2-3