Summation

[Alan]

I have just bought Formulaic or iPhone but apparently it will not
serve me (at least not yet...). I have many equations based on
summations for which I need a solver. From what I see, there is no
summation in Formulaic. For example, I might need to enter the
following equation:

PV = FV/(1+i)ˆn + [PMT/(1+i)ˆ1 + PMT/(1+i)ˆ2 + PMT/(1+i)ˆ3 + ... + PMT/
(1+i)ˆ(n-1) + PMT/(1+i)ˆn]

I don't see how this can be done without a summation (Sigma) function.
With the summation function, this could be input as:

PV = FV/(1+i)ˆn + Summation for t valuing from 1 to n of [PMT/(1+i)ˆt]

Am I mistaken in that this can already be done currently? If not, do
you plan on including the summation (or Sigma) function in Formulaic?

Thank you,
Alan

[hoymoon]

Hello Alan,

Thank you for your interest in Formulaic.

There is no summation function in the current version of Formulaic.

The type of problem you gave as an example is however something you
can solve with Formulaic by rewriting the equation. For some examples,
please take a look at the "Finance" group of equations in the built-in
library. There are equations for Future Value, Present Value, and Bond
Price, which compute something quite similar to your example, but with
the non-recurring-term version of the equation. As long as you are
dealing with a fixed payment amount, the equation can be rewritten in
this way (there isn't currently an easy way to deal with differing
cash flows in Formulaic).

Both "Time Value of Money" or "Bond Mathematics" can include details
on how to rewrite certain cases of the summation into an algebraic
equation. For some additional background, you could also visit:
en.wikipedia.org/wiki/Future_value

More built-in functions are on the to-do list for future versions of
Formulaic, and these will include additional financial functions. A
general purpose summation function is a lot more complex to implement
because of the implied recursion (the expression in the summation
function has to be evaluated many times as part of the whole equation
having to be evaluated many times to search for a solution).

Kind regards,
Hoy Moon