Lagrangian Interpolation of Three Points for HP25

This program was written by Walter Gray and is used here by permission.

This program is supplied without representation or warranty of any kind. The author and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

Instructions

Step	Instructions	Input Data/Units	Keys	Output Data/Units
1	Enter program
2	Store 3 sets of x,y coords in registers 0-5
		x1	STO 0
		y1	STO 1
		x2	STO 2
		y2	STO 3
		x3	STO 4
		y3	STO 5
4	Store X	X	STO 6
5	Compute Y		f PRGM R/S	Y
4	For new case, go to step 2

Example

X1=-11 Y1=121 X2=3 Y2=9 X3=2 Y3=4
X=2.5 Y=6.25 etc

The Program

LINE  KEYS
 00
 01   RCL 1
 02   RCL 0
 03   RCL 2
 04   -
 05   ÷
 06   RCL 1
 07   RCL 0
 08   RCL 4
 09   -
 10   ÷
 11   -
 12   STO 7
 13   RCL 3
 14   RCL 0
 15   RCL 2
 16   -
 17   ÷
 18   STO - 7
 19   RCL 3
 20   RCL 6
 21   RCL 2
 22   -
 23   ÷
 24   STO + 7
 25   RCL 5
 26   RCL 0
 27   RCL 4
 28   -
 29   ÷
 30   STO + 7
 31   RCL 5
 32   RCL 6
 33   RCL 4
 34   -
 35   ÷
 36   STO - 7
 37   1
 38   RCL 6
 39   RCL 2
 40   -
 41   ÷
 42   1
 43   RCL 6
 44   RCL 4
 45   -
 46   ÷
 47   -
 48   STO ÷ 7
 49   RCL 7     ; Displays Y

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