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Full Discussion: Script for finding standard deviation
Top Forums Shell Programming and Scripting Script for finding standard deviation Post 302235248 by jim mcnamara on Thursday 11th of September 2008 12:27:07 PM
Old 09-11-2008
You are correct. I copied your algorithm - it needs checks.

Code:
awk -F','  '{ sum=0; sumsq=0;
                for(i=1; i<=NF;i++) {sum+=$i; sumsq+=$i*$i}
                printf("mean=%f  stddev= %f\n", sum/NF, 
                sqrt(  ( (sumsq - (sum*sum))< 0) 
                           ? sumsq - (sum*sum)*-1 : sumsq -(sum*sum) )
              } ' file.csv

This should prevent domain errors.... the fact that there are a lot of zero values means the sum of squares can be very small number. You could also use a function like this placed at the top of the awk code block
function abs(n) { return (n <0)? n*=-1 : n}


Code:
awk -F','  '{ function abs(n) { return (n <0)? n*=-1 : n}

                sum=0; sumsq=0;
                for(i=1; i<=NF;i++) {sum+=$i; sumsq+=$i*$i}
                printf("mean=%f  stddev= %f\n", sum/NF, sqrt(abs(sumsq - (sum*sum))) )
              } ' file.csv

 

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LEARN ABOUT CENTOS

zlassq

zlassq.f(3)							      LAPACK							       zlassq.f(3)

NAME

       zlassq.f -

SYNOPSIS

   Functions/Subroutines
       subroutine zlassq (N, X, INCX, SCALE, SUMSQ)
	   ZLASSQ updates a sum of squares represented in scaled form.

Function/Subroutine Documentation
   subroutine zlassq (integerN, complex*16, dimension( * )X, integerINCX, double precisionSCALE, double precisionSUMSQ)
       ZLASSQ updates a sum of squares represented in scaled form.

       Purpose:

	    ZLASSQ returns the values scl and ssq such that

	       ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,

	    where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
	    assumed to be at least unity and the value of ssq will then satisfy

	       1.0 .le. ssq .le. ( sumsq + 2*n ).

	    scale is assumed to be non-negative and scl returns the value

	       scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
		      i

	    scale and sumsq must be supplied in SCALE and SUMSQ respectively.
	    SCALE and SUMSQ are overwritten by scl and ssq respectively.

	    The routine makes only one pass through the vector X.

       Parameters:
	   N

		     N is INTEGER
		     The number of elements to be used from the vector X.

	   X

		     X is COMPLEX*16 array, dimension (N)
		     The vector x as described above.
			x( i )	= X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.

	   INCX

		     INCX is INTEGER
		     The increment between successive values of the vector X.
		     INCX > 0.

	   SCALE

		     SCALE is DOUBLE PRECISION
		     On entry, the value  scale  in the equation above.
		     On exit, SCALE is overwritten with the value  scl .

	   SUMSQ

		     SUMSQ is DOUBLE PRECISION
		     On entry, the value  sumsq  in the equation above.
		     On exit, SUMSQ is overwritten with the value  ssq .

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   September 2012

       Definition at line 107 of file zlassq.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       zlassq.f(3)
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