Sum

Returns the sum of array X over the dimension indexed by variable I. You can also sum over multiple indexes:

Sum(A, I, J, K)

It treats any Null values in A as zero.

Sum(a: Array[i]; i: ... optional Index; IgnoreNonNumbers, IgnoreNaN: Optional Boolean)

Set IgnoreNaN to treat NaN, indeterminate numeric values, as zero. Normally NaNs propagate through a model -- Sum(x, i) returns NaN if any value in x is NaN. This can help tracking down numeric problems in your logic, such as 0/0 or Sqrt(-1). But if you know there are NaNs that you want to ignore, set IgnoreNaN parameter to True (1).

Sum(A, I, IgnoreNaN: True)

Similarly, set optional parameter IgnoreNonNumbers to True, to treat non-numeric values such as text or references, as zero, e.g.:

Sum(A, I, J, IgnoreNonNumbers:true)

You must use named parameter syntax to use IgnoreNonNumbers and IgnoreNaN, as shown in the above examples.

Compare:

X := Array(I,[5,6,'X',7])
IgnoreWarnings(Sum(X,I)) → "11X7" 
Sum(X,I,IgnoreNonNumbers: True) → 18

In older releases, you could use Sum to concatenate text, if all or some of the values are text. We strongly discourage this usage. It still works for backward compatibility, but gives a warning. Use the JoinText function instead to make it clear you want to join (concatenating) text -- not just summing over values, some of which turn out to be text inadvertently.

A straight sum over X results in a warning to this effect, but the functionality is still supported for legacy reasons. In that case, (5+6+'X'+7) evaluates as ( ( (5+6)&'X' ) & 7 ). In the second example, numbers are ignored so only the numbers, 5+6+7, are added.

Using Sum to add arrays

With Intelligent Arrays, you can of course add two arrays with the "+" operator:

a1 + a2

You can also Sum to do this:

Sum([a1, a2])

In this example, the I parameter is omitted, and it automatically Sums over the implicit index of the list [a1, a2]. These two methods are equivalent except for <<null>> values: Sum([a1, a2]) treats any <<null>> values as zero. But

a1 + a2

returns <<null>> if any values to be added are <<null>>.

See Also

• Cumulate
• Product