Erlang Library for Excel

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Erlang Worksheet Functions Reference

About the Erlang Functions

The Erlang Library for Excel from Abstract Micro Systems contains definitions of several functions that you can use in your Excel worksheets.  Extensive help is available: each function has its own help topic page in this help file, and all the functions are listed in Excel's Function Dialog under the category "Erlang Library for Excel", or under the category "Compatability".

These functions perform calculations in the Erlang B and Erlang C queueing models.  We've designed the library for convenient everyday use by telecommunications analysts, with special emphasis on features useful in staffing and performance computations for call centers.

List of Functions

Name Description
ErlbBlockage ErlbBlockage( nsrv, trafficInErlangs)

Returns the Erlang B blockage for a specified number of servers and specified offered traffic.

ErlbNsrvFromBlockage ErlbNsrvFromBlockage( blockageFraction, trafficInErlangs)

Returns the number of servers that will experience the specified blockage given a specified offered load

ErlbTrafFromBlockage ErlbTrafFromBlockage( blockageFraction, nsrv)

Returns the traffic load in erlangs that will produce the specified blockage for the specified number of servers, in the Erlang B queueing model.

ErlcFractionDelayed ErlcFractionDelayed(nsrv, trafficInErlangs)

Returns the probability that a customer arriving at the queueing facility will experience a delay before beginning service.

ErlcFractionOk ErlcFractionOk( nsrv, trafficInErlangs, ahtSeconds, okWaitSeconds)

Returns the fraction of customers who begin service after waiting no longer than the specified number of seconds, for the given number of servers, traffic load, and average handle time.

ErlcNsrvFromFractionOk ErlcNsrvFromFractionOk( trafficInErlangs, ahtSeconds, okWaitSeconds, fractionOk)

Returns the number of servers needed to carry a specified traffic load with a specified service level.

ErlcNsrvFromFractionOk5 ErlcNsrvFromFractionOk5( secondsPerPeriod, callsPerPeriod, ahtSeconds, okWaitSeconds, fractionOk)

Returns the number of servers needed to carry a specified traffic load with a specified service level.

ErlcNsrvFromWait ErlcNsrvFromWait( trafficInErlangs, ahtSeconds, averageWaitSeconds)

Returns the number of servers required to achieve a desired average wait time in the Erlang C queueing model.

ErlcNsrvFromWait4 ErlcNsrvFromWait4( secondsPerPeriod, callsPerPeriod, ahtSeconds, averageWaitSeconds)

Returns the number of servers required to achieve a desired average wait time in the Erlang C queueing model.

ErlcNwaiting ErlcNwaiting( nsrv, trafficInErlangs)

Returns the average number of waiting customers (also called the average queue length) in the Erlang C queueing model, for a given number of servers and given traffic load.

ErlcNwaiting4 ErlcNwaiting4( nsrv, secondsPerPeriod, callsPerPeriod, ahtSeconds)

Returns the average number of waiting customers (also called the average queue length) in the Erlang C queueing model.

ErlcTrafFromFractionOk ErlcTrafFromFractionOk(nsrv, ahtSeconds, okWaitSeconds, fractionOk)

Returns the erlangs of traffic that can be carried by a specified number of servers, at a specified service level in the Erlang C queueing model.

ErlcTrafTromWait ErlcTrafFromWait( nsrv, ahtSeconds, averageWaitSeconds)

Returns the traffic load in erlangs that can be carried by a given number of servers, with a given average handle time, and with a given average wait time.  Assumes the Erlang C queueing model.

ErlcWait ErlcWait( nsrv, trafficInErlangs, ahtSeconds)

Returns the average wait in seconds in the Erlang C queueing model, for a given number of servers, a given offered traffic, and a given average handle time.

ErlcWait4 ErlcWait4( nsrv, secondsPerPeriod, callsPerPeriod, ahtSeconds)

Returns the average wait in seconds in the Erlang C queueing model, for a given number of servers, period length, number of calls per period, and average handle time.

Mathematical Properties of the Functions

  1. All function arguments should be numbers greater than or equal to 0
  2. Supplying a negative number as an argument will not produce an error, but the return value will be meaningless.
  3. No function argument is required to be a whole number.  Even the nsrv arguments (representing a number of servers) may contain digits after the decimal point, and the fractional part of the argument will affect the return value of the function.
  4. Any argument whose name contains the word "fraction" should be between 0 and 1 (inclusive).  Supplying a value outside this range will not produce an error, but the return value will be meaningless.
  5. All return values are greater than or equal to 0.

Using the Functions in Excel

  1. Use the Erlang functions exactly as you would any of Excel's built-in functions.
  2. As with any numeric function in Excel, each argument may be a number or an expression that evaluates to a number.  Of course, these expressions may contain references to worksheet cells.
  3. Obtain quick help on any Erlang function by locating it in the Excel Function Dialog (press the "fx" button) under the category "Erlang Library for Excel".  Click here for details.
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