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Evalstring on math equation

nosaj

How do you evaluate mathematical equation in string that evalstring can’t handle without parsing/processing the string?

 evalstring("(3 -1)*2")           

*Error* eval: not a function – 3

 

evalstring("(5e10u)*0.25u")

*Error* eval: not a function - 50000.0

 Thanks

  • Both of your expressions contain issues, as reported. The first string has no space after the '-' and thus it looks to SKILL like (functionName -1) => functionName(-1), i.e. a function being called with a single argument which happens to be negative: 3(-1) . Put a space in after the minus sign and it should be fine. In the second expression "5e10u" does not need to be surrounded with parentheses, again it looks like you are calling a function, this time with no argument: 50000.0(). You can use unwindProtect() or errset() to wrap around expressions that might cause issues during evaluation, then you can programmatically decide what to do if an error is encountered.
    Best regards,
    Lawrence.
  • Thank you for the explanation and suggestion.

  • If the mathematical expression is limited to the operators and functions supported in AEL (Analog Expression Language) you could do:

    env=aelEnvCreate("f" nil nil)
    aelEnvInterpret(env "(3 -1)*2")  ; outputs "4.0"
    aelEnvInterpret(env "(5e10u)*0.25u") ; outputs "12.5e-3"

    Note you could call aelNumber() on the result of aelEnvInterpret to return a number. Or you might want to use aelPushSignifDigits if you want to increase the precision.

    However, note that AEL is not the same as SKILL.

    Andrew.

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