Interp

Syntax

Interp(Year1, Value1, Year2, Value2,... YearN, ValueN, [GrowthRate]) or
Interp(ExcelFilename, ExcelRangeName, [GrowthRate])

Description

Calculates a value in any given year by linear interpolation of a time-series of year/value pairs.

Using the above two alternatives syntaxes year/value pairs can either be entered explicitly or linked to a range in an Excel spreadsheet. Use the WEAP Yearly Time-series Wizard to input these values or specify the Excel data. In either case, years do not need to be in any particular order, but duplicate years are not allowed, and must be in the range 1990-2200. The final optional parameter to the function is a growth rate that is applied after the last specified year. If no growth rate is specified zero growth is assumed (i.e. values are not extrapolated).

When linking to a range in Excel, you specify the full path name of a valid Excel worksheet or spreadsheet (an XLS or XLW) file, followed by a valid Excel range. A range can be either a valid named range (e.g. "Import") or a range address (e.g. "Sheet1!A1:B5"). The Excel range must contain pairs of years and values in its cells arranged into 2 columns. Use the Yearly Time-series Wizard to select a worksheet, to choose among the valid named ranges in the worksheet, and to preview the data that will be imported.

Example

Interp(2000, 10.0, 2010, 16.0, 2020, 30.0, 2%)

2000 = 10.0
2005 = 13.0
2020 = 30.0
2021 = 30.6

Tips

Use the Yearly Time-Series Wizard to enter the data for this function.
You may also import many data expressions at once from Excel. See Export to Excel, Import from Excel for details.