plot and evaluate this cubic polynomial

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enzo milito
enzo milito 2014-5-15
评论： Benjamin Avants 2014-5-16
I need to evalue this polynomial q(t) = a + b(t - tk1) + c(t - tk1)^2 + d(t - tk1)^3
whit tk1<t<tk2
where a,b,c,d,tk1,tk2 are costant
I think to polyval but it is rigth for : q(t) = a + b*t + c*t^2 + d*t^3 how can evalue and plot my polynomial
thanks

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Benjamin Avants
Benjamin Avants 2014-5-15
I think the easiest thing to do is to first define t as a vector. Choose your resolution and invoke linspace:
numberOfPoints = 1000;
t = linspace(tk1,tk2,numberOfPoints);
then compute q and plot:
q = a + b .* (t - tk1) + c .* (t - tk1).^2 + d .* (t - tk1).^3;
plot(t,q);
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enzo milito
enzo milito 2014-5-15
I tryed your suggestion and run very well, but now I have connect or concatenate two or more different polynomial in different interval time tk1-tk2 tk2-tk3 tk3-tk4 for to obtain one plot from tk1-tk4 and so have you any suggestion ? thanks
Benjamin Avants
Benjamin Avants 2014-5-16
There are a couple of approaches that will accomplish this. I think the best way is to simply compute each segment for the desired polynomial and then do the following:
combinedQ = [q1,q2,q3];
or
combinedQ = [q1;q2;q3]; % depending on whether q is a row or column vector
and then
totalT = [t1,t2,t3]; % Once again, use semicolons if this doesn't work
plot(totalT,combinedQ);

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