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DEPRECIATE STRAIGHTLINE is used to compute straight line depreciation on an investment stream str over some depreciation lifetime dtime.  Depreciation is computed by lumping all payments made within the fiscal period specified by fisc together.  You can also specify an initial value for stream that will initialize the different accumulations as if the function had been called with a constant value of init in place of the str argument over the previous dtime.  This means that if str continues to take on the value init that the output of the function will continue to be constant at that value.

To use this function dtime must be an integer multiple of fisc.  If it is not Vensim will automatically adjust it so that it is.  The ratio of dtime/fisc determines the number of different fiscal periods that are involved.  For an investment made at a particular time, DEPRECIATE STRAIGHLINE will return dtime/fisc of that investment in the first fiscal period and each that follows.  To guarantee that this will work the function actually includes dtime/fisc of the current value of str in its returned value.  This can lead to somewhat odd behavior when there is a decrease in the value of str within a fiscal period, but  guarantees that all outflows will occur in the correct fiscal periods.  

Restrictions:  Must appear directly following the equal sign = and not be followed by anything else.

The DEPRECIATE STRAIGHTLINE function creates a variable that acts like both an Auxiliary and a Level.  The return value depends on the current value of str, and also on its past values.  

The output units are the same as the units of the first argument and must also match the initial quantity units.  The depreciation time dtime has the same units as time while fisc converts from time units to fiscal time units (eg 12 Month/Year).  The fiscal time units are not used elsewhere.

Availability: Not PLE or PLE Plus.

See also: DEPRECIATE BY SCHEDULE

Sample model: DEPRECIATE STRAIGHTLINE.mdl in FunctionExamples