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Question

polyfit command

jom09 (Mechanical)

(OP)

25 Aug 09 05:54

Hi guys, i am currently trying to use matlab to find an equation of a curve.

The curve is speed (x axis) Vs torque (y axis)

The cordinates for the speed are (0, 20, 40, 60, 65, 70, 75, 80, 85, 90, 95, 100)

The coordinates for the torque are (150, 176, 212, 268, 282, 282, 289, 296, 290, 262, 200, 100, 0)

What i want to do is use this information to find out the equation of this curve, preferably in the form of Torque = soem function of speed.

Any help on this would be much appreciated.

Thanks

MikeyP (Aerospace) · Answer 1 · 2009-08-25 06:16:12

1. Type "help polyfit"
2. Why not just use the curve fitter in Excel?

M

--
Dr Michael F Platten

electricpete (Electrical) · Answer 2 · 2009-08-25 19:47:10

also there is a choice fitting or generating a spline. Spline exactly matches the data, for use when piecewise solution is acceptable and you suspect no error in the data. Fit works when you have error in the data or want a simpler expression (not a piecewise expression).

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electricpete (Electrical) · Answer 3 · 2009-08-25 19:47:54

and in either case, your two vectors need to be the same length (yours aren't)

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jom09 (Mechanical) · Answer 4 · 2009-08-25 23:49:00

Thanks, for that electricpete, the vecotors are meant to eb the same there was justa typo n there is an extra 282 in the torques. So how would i go about typing code into matlab to exactly match the data and get a equation?

Thanks

GregLocock (Automotive) · Answer 5 · 2009-08-26 00:25:05

Well, the way I'd do it is to find someone who had done the turorials or was paying attention in class, and actually knew how to use matlab, and ask them to do it.

Of course I might have to pay them to do my work for me. Such is life.

Cheers

Greg Locock

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electricpete (Electrical) · Answer 6 · 2009-08-26 00:35:19

What Greg said. If you want the spline, look at
help spline
and
help unmkpp

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