Value ± Error rounding

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Thu, 02/21/2013 - 07:46 am

I have a problem that I am trying to solve. Can anyone help me please?

I have as an input a value and its error (uncertainty). I want to create a string that is the Value ± Error but with appropriate rounding on both numbers. By appropriate rounding, I mean 2 significant figures in the error value.

I have written the following function that does mostly does this, but has some exceptions to which I am struggling to find a simple resolution.

Function/S FormatValueError(vVal,vErr)
    variable vVal
    variable vErr
    // Return string containing value ± error rounded to 2 sf on error
    // or "" if there was a problem
    string sValErr = ""
    string sVal,sErr
    variable vPower
    do
        if( numType(vVal) == 2) //NaN
            break // return empty string
        endif
        if( (numType(vErr) == 2) || (vErr == 0) ) // NaN or zero
            sprintf sValErr, "%g", vVal // just return vVal
            break
        endif
        // Find power 10 of Error
        variable vErrPower = floor( log( abs(vErr) ) )
        vErrPower -= 1 // go to 2 sf
        // Find power 10 of Value
        variable vValPower = floor( log( abs(vVal) ) )
        if( vValPower < vErrPower ) // catch value less than error
            vPower = vValPower - 1 //round to 2 sf in Value
        else
            vPower = vErrPower // round to 2 sf in Error
        endif
        // Now do the rounding
        vVal=sign(vVal) * (10 ^ vPower) * round( abs(vVal) * (10 ^ (-vPower) ) )
        sprintf sVal,"%g",vVal
        vErr=sign(vErr) * (10 ^ vPower) * round( abs(vErr) * (10 ^ (-vPower) ) )
        sErr=num2str(vErr)
        sprintf sErr,"%g",vErr
        // assemble the result
        sValErr = sVal
        if( strLen(sErr) > 0)
            sValErr += " ± " + sErr
        endif
        break
    while(1)
    return sValErr
End


For example:
print FormatValueError(123.456,7.123456)
gives 123.5 ± 7.1 (correct)

print FormatValueError(1.008,0.111)
gives 1.01 ± 0.11 (correct)

print FormatValueError(1.0008,0.111)
gives 1 ± 0.11 (no - I would like to get 1.00 ± 0.11)

print FormatValueError(123.456E-4,1.345678E-5)
gives 0.012346 ± 1.3e-05 (no - I would like 0.012346 ± 0.000013 or 1234.6e-5 ± 1.3e-5)

Is there a cunning way of achieving the last two results without doing a heavy handed look for each type of number format and deal with each foreseeable situation bit by bit?

Thank you,
Kurt
KurtB wrote:

Is there a cunning way of achieving the last two results without doing a heavy handed look for each type of number format and deal with each foreseeable situation bit by bit?


Try printf and sprintf.

February 21, 2013 at 07:56 am - Permalink