Page 303 - Numerical Analysis Using MATLAB and Excel

Interpolation with MATLAB

V I
-2.000 -0.0330 0.20
0.15
-1.975 -0.0326
0.10
-1.950 -0.0323 0.05
-1.925 -0.0320 0.00
-1.900 -0.0316 -0.05
-2 -1 0 1 2 3 4 5
-1.875 -0.0313
-1.850 -0.0309 A B
-1.825 -0.0306 8 -1.8500 -0.0309266
-1.800 -0.0302 9 -1.8250 -0.0305803
-1.775 -0.0299
-1.750 -0.0295 =VLOOKUP(-1.8375,A2:B282,2) = -0.030927
-1.725 -0.0292 =VLOOKUP(-1.8375,A2:B282,2,TRUE) = -0.030927
-1.700 -0.0288 =VLOOKUP(-1.8375,A2:B282,2,FALSE) = #N/A
-1.675 -0.0285
-1.650 -0.0281 A B
-1.625 -0.0277 264 4.5500 0.1484323
-1.600 -0.0274 265 4.5750 0.1496775
-1.575 -0.0270
-1.550 -0.0267 =VLOOKUP(4.5535,A2:B282,2) = 0.1484323
-1.525 -0.0263
Figure 7.5. Using the Excel VLOOKUP function for interpolation

2. interp1(x,y,x ,’method’) performs the same operation as interp1(x,y,x ) where the string
i
i
method allows us to specify one of the methods listed below.
nearest − nearest neighbor interpolation

linear − linear interpolation; this is the default interpolation
spline − cubic spline interpolation; this does also extrapolation

cubic − cubic interpolation; this requires equidistant values of x
3. interp2(x,y,z,x ,y ) is similar to interp1(x,y,x ) but performs two dimensional interpolation;
i
i
i
4. interp2(x,y,z,x ,y ,’method’) is similar to interp1(x,y,x ,’method’) but performs two dimen-
i
i
i
sional interpolation. The default is linear. The spline method does not apply to two dimen-
sional interpolation.
We will illustrate the applications of these functions with the examples below.

Numerical Analysis Using MATLAB® and Excel®, Third Edition 7−25
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