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SergioSolimena's avatar
SergioSolimena
Copper Contributor
Apr 04, 2019

A case of wrong formula calculation in Excel?

I like to have your opinion on the formula calculation performed by Excel in a particolar case that surprised me very much. This is the case. A(1,1) =5 A(2,1) = - A1^2 Excel display result in A(2...
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Detlef_Lewin's avatar
Detlef_Lewin
Silver Contributor
Apr 04, 2019

SergioSolimena 

Check the order of operation with formula evaluation.

-A1^2 -> -5 -> -5^2 -> 25

-(A1^2) -> -(5^2) -> -(25) -> -25

 

  • SergioSolimena's avatar
    SergioSolimena
    Copper Contributor
    Apr 04, 2019
    What you says is clear but it's not correct because in the formula y=-x^2 the result is always negative for any x different from zero.
    I don't have to use the parenthesis.
    As I shown in the example, the same formula y= -A^2 +A =+A- A^2 is written in two different way, only changing the position af the two addendum. The result must be exactly the same. But this not what Excel does.
    This means that it necessary to put attention at the order of the addendum in a sum, and this violates the commuted property of the terms of the sum.
    Because now I know this question I put always attention when i write a formula, but in a complex problem this not simple and reliable.
    • Detlef_Lewin's avatar
      Detlef_Lewin
      Silver Contributor
      Apr 05, 2019

      SergioSolimena 

      *

      SergioSolimena wrote:
      As I shown in the example, the same formula y= -A^2 +A =+A- A^2 is written in two different way, only changing the position af the two addendum. The result must be exactly the same. But this not what Excel does.
      *

      As you can see in the table provided by PeterBartholomew1 the - (minus sign) in the first case is a negation (a lower order then ^) and in the second case a subtraction (a higher order then ^).

      So by putting parenthesis around A^2 you are changing the order of operation:

      -(A^2)+A = +A-(A^2)

       

      • SergioSolimena's avatar
        SergioSolimena
        Copper Contributor
        Apr 05, 2019
        Detlef_Lewin wrote:
        As you can see in the table provided by PeterBartholomew1 the - (minus sign) in the first case is a negation (a lower order then ^) and in the second case a subtraction (a higher order then ^.
        -
        Thanks for the reply.
        The Excel rules are clear but unfortunately they are different, in this particular case, from the mathematical rules. This can generate an unexpected result and you have to be careful.
        Thanks again.
  • PeterBartholomew1's avatar
    PeterBartholomew1
    Silver Contributor
    Apr 04, 2019

    Detlef_Lewin

     

    The help page shows the operator precedence to be as shown in the following table.

    If in doubt, a pair of parentheses work wonders!

     

    Operator

    Description

    : (colon)

    (single space)

    , (comma)

    Reference operators

    –

    Negation (as in –1)

    %

    Percent

    ^

    Exponentiation

    * and /

    Multiplication and division

    + and –

    Addition and subtraction

    &

    Connects two strings of text (concatenation)

    =
    < >
    <=
    >=
    <>

    Comparison

     

     

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