Page 414 - Excel for Scientists and Engineers: Numerical Methods

APPENDIX 3 CUSTOM FUNCTIONS HELP FILE 391

InterpL
Performs linear interpolation in a table of x- and y-values. Returns the interpolated y-
value corresponding to a specified x-value.

Syntax
Inter p L( lookup- value, kno wn-x Is, known- y ‘s)
lookup-value the x-value for which you want to find the interpolated y-value
kno wn-x ‘s the range of x-values in the table (independent variable)
known- y ‘s the range of y-values in the table (dependent variable)

Remarks
The argument lookup-value can be either a number or a reference to a cell that
contains a number.
The arguments known-x’s and known-y’s can be either a reference to a range of
cells or a named range.
The function cannot handle implicit references; that is, a name or range reference
cannot be used for a range of lookup values.
The table of x- and y-values must be arranged in ascending order of x-values.
The table of x- and y-values can be either either horizontal or vertical.
The function cannot be used for extrapolation. A lookup value that is either greater
than or less than the range of x-values returns #REF!.
The linear interpolation formula is:

where x is the lookup value and xo and x1 are the values in the table that bracket
the lookup value; xo is the value in the table that is equal to or less than
lookup- value.

Example
The expression InterpL(33.3,$A$3:$A$47,$B$3:$B$47) where $A$3:$A$47 is the range
containing the independent or x-values and $B$3:$B$47 is the range containing the
dependent or y-values.

See Also
InterpC, InterpC2