fit a first,second,and third degree polynomial, and determine the respective regression co-efficients.

i am new to matlab and just need an example to follow, please help Please see attached. thanx

i attempted the first part, plz help with regression...

Time = [1,2,3,4,5,6,7,8,9,10];

Pressure = [26.1,27.0,28.2,29.0,29.8,30.6,31.1,31.3,31.0,30.05];

New_Time = 0:0.5:10;

newf1 = polyval(polyfit(Time,Pressure,1),New_Time);
newf2 = polyval(polyfit(Time,Pressure,2),New_Time);
newf3 = polyval(polyfit(Time,Pressure,3),New_Time);

plot(Time,Pressure,'o',New_Time,newf1,New_Time,newf2,New_Time,newf3)
title('Fit of Pressure Samples')
xlabel('Sample Interval,sec')
ylabel('Pressure, PSI')
legend('Data','Linear Fit','Quadratic Fit','Cubic Fit') % linear is first order, quadratic is second order and cubic is third order

[John D'Errico]

READ THE GETTING STARTED TUTORIALS. Being new is irrelevant. You won't learn a thing until you start making an effort.

[james bond]

i was working on it i think i got the first part ,i have no idea what to do for the regression....HELP !

Answer 1

[KSSV]

R3 = polyfit(Time,Pressure,3) ;

Gives the coefficients of the polynomial. In this case coefficients of third degree polynomial.

[james bond]

an equation for the regression was given , please take a look at the attached pic. https://www.mathworks.com/matlabcentral/answers/uploaded_files/97341/image.png

[KSSV]

You may refer any Numerical Methods using MATLAB book..you will find code with explanation in there.

[John D'Errico]

No. In the picture that you show, the equation shows how to compute R^2. You already have the regression, given by polyfit.

[james bond]

SO the values outputed by polyfit "R3 = polyfit(Time,Pressure,3) ;" is the regression co-efficients being asked for ? i dont have to somehow use the R^2 formula in the pic attached ?

[John D'Errico]

Calling R^2 a "regression coefficient" is spectacularly poor terminology on the part of the person who wrote that assignment. But, yes, if you need to compute R^2, then you need to use the formula.

[james bond]

wow, how do i do that with that formula in matlab ?