[GRASS-dev] r.regression.line crash in awk (awk debugging)

[Markus Neteler]

On Fri, Aug 7, 2009 at 3:05 AM, Hamish<hamish_b at yahoo.com> wrote:
> Markus Neteler wrote:
>> I wanted to run a linear regression on a DEM and a temperature
>> map but got an error:
>> awk: cmd. line:2: (FILENAME=- FNR=3) fatal: division by zero attempted
>>
>> I have reduced everything to this part (added --lint):
>>
>> #!/bin/sh
>>
>> unset LC_ALL
>> LC_NUMERIC=C
>> export LC_NUMERIC
>>
>> echo "345.551054 1 1
>> 364.229489 1 1
>> 382.907925 1 3" | awk --lint '{tot += $3;sumX +=$1 * $3;
>> sumsqX
>> +=$1*$1*$3;sumY +=$2 * $3; sumsqY +=$2*$2*$3; sumXY
>> +=$1*$2*$3;}
>> END {B=(sumXY - sumX*sumY/tot)/(sumsqX - sumX*sumX/tot);
>> R= (sumXY - sumX*sumY/tot)/((sumsqX - sumX^2/tot)*(sumsqY -
>> sumY^2/tot))^0.5;
>> mediaX=sumX/tot;sumsqX=sumsqX/tot;varX=sumsqX-(mediaX^2);sdX=varX^0.5;
>> mediaY=sumY/tot;sumsqY=sumsqY/tot;varY=sumsqY-(mediaY^2);sdY=varY^0.5;
>> A=mediaY - B*mediaX; F= R^2/(1-R^2/tot-2);
>> print A, B, R, tot, F, mediaX, sdX, mediaY, sdY}'
>>
>> Running this, I get:
>> awk: (FILENAME=- FNR=1) warning: reference to uninitialized
>> variable `tot'
> ....
>
>
> it starts with "tot += $3" [aka "tot = tot + $3"], but tot is unused at
> that point so undefined. (maybe awk can be trusted to always init new
> vars to 0? no idea)
>
> adding a 'BEGIN { tot = 0; sumX = 0; ... }' section at the start of the
> awk script might help.

Tried this:

echo "345.551054 1 1
364.229489 1 1
382.907925 1 3" | awk --lint -F " " 'BEGIN { tot = 0; sumX = 0; sumsqX
= 0; sumY = 0; sumsqY = 0; sumXY = 0;}
    {tot += $3; sumX +=$1*$3; sumsqX +=$1*$1*$3; sumY +=$2*$3; sumsqY
+=$2*$2*$3; sumXY +=$1*$2*$3;}
END { B     = (sumXY - sumX*sumY/tot)/(sumsqX - sumX*sumX/tot);
      R     = (sumXY - sumX*sumY/tot)/((sumsqX - sumX^2/tot)*(sumsqY -
sumY^2/tot))^0.5;
      mediaX= sumX/tot; sumsqX=sumsqX/tot; varX=sumsqX-(mediaX^2); sdX=varX^0.5;
      mediaY= sumY/tot; sumsqY=sumsqY/tot; varY=sumsqY-(mediaY^2); sdY=varY^0.5;
      A     = mediaY - B*mediaX; F= R^2/(1-R^2/tot-2);
      print A, B, R, tot, F, mediaX, sdX, mediaY, sdY}'

but
awk: cmd. line:3: (FILENAME=- FNR=3) fatal: division by zero attempted

Confused,
Markus