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Full Discussion: Python: make dual vector dot-product more pythonic
Top Forums Shell Programming and Scripting Python: make dual vector dot-product more pythonic Post 303041217 by figaro on Monday 18th of November 2019 04:18:23 PM
Old 11-18-2019
Python: make dual vector dot-product more pythonic
I have this dot product, calculating weighted means, and is applied to two columns in a list:
Code:
# calculate weighted values in sequence
for i in range(len(temperatures)-len(weights)):
  temperatures[i].append(sum([weights[j]*temperatures[i+j][5] for j in range(len(weights))]))
  temperatures[i].append(sum([weights[j]*temperatures[i+j][6] for j in range(len(weights))]))

The calculation is a running dot-product, ie the list of temperature samples is far larger than the list of weights, hence the correction of subtracting len(weights) at the end of the main loop.
This traverses the list of weights twice, which is inefficient and degrades performance. How could this be done in a more pythonic way?

I also have concerns about the main loop. Would this be considered more pythonic?:
Code:
# calculate weighted values in sequence
for i in range(len(temperatures)):
   try:
      # weighted calculation here
   except:
      # do nothing, because array out of bounds

Last edited by figaro; 11-18-2019 at 06:01 PM.. Reason: Emphasise the fact that the lists are not of the same length, ie the dot product calculates a running weighted mean.
 

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LEARN ABOUT SUNOS

mlib_vectordotprod_s8c_sat

mlib_VectorDotProd_U8_Sat(3MLIB)			    mediaLib Library Functions				  mlib_VectorDotProd_U8_Sat(3MLIB)

NAME

       mlib_VectorDotProd_U8_Sat,  mlib_VectorDotProd_U8C_Sat,	mlib_VectorDotProd_S8_Sat, mlib_VectorDotProd_S8C_Sat, mlib_VectorDotProd_S16_Sat,
       mlib_VectorDotProd_S16C_Sat, mlib_VectorDotProd_S32_Sat, mlib_VectorDotProd_S32C_Sat - vector dot product (inner product)

SYNOPSIS

       cc [ flag... ] file... -lmlib [ library... ]
       #include <mlib.h>

       mlib_status mlib_VectorDotProd_U8_Sat(mlib_d64 *z, const mlib_u8 *x, const mlib_u8 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_U8C_Sat(mlib_d64 *z, const mlib_u8 *x, const mlib_u8 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_S8_Sat(mlib_d64 *z, const mlib_s8 *x, const mlib_s8 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_S8C_Sat(mlib_d64 *z, const mlib_s8 *x, const mlib_s8 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_S16_Sat(mlib_d64 *z, const mlib_s16 *x, const mlib_s16 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_S16C_Sat(mlib_d64 *z, const mlib_s16 *x, const mlib_s16 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_S32_Sat(mlib_d64 *z, const mlib_s32 *x, const mlib_s32 *y, mlib_s32 n);

       mlib_status mlib_VectorDotProd_S32C_Sat(mlib_d64 *z, const mlib_s32 *x, const mlib_s32 *y, mlib_s32 n);

DESCRIPTION

       Each of these functions computes the dot product of two vectors, defined by the following equation:

       Z = X . Y*

       where Y* is the conjugate of the Y vector.

       For real data, the following equation is used:

	      n-1
       z[0] = SUM (x[i]*y[i])
	      i=0

       For complex data, the following equation is used:

	      n-1
       z[0] = SUM (x[2*i]*y[2*i] + x[2*i + 1]*y[2*i + 1])
	      i=0

	      n-1
       z[1] = SUM (x[2*i + 1]*y[2*i] - x[2*i]*y[2*i + 1])
	      i=0

PARAMETERS

       Each of the functions takes the following arguments:

       z	       Pointer to the dot product of the two vectors.

       x	       Pointer to the first element of the first source vector.

       y	       Pointer to the first element of the second source vector.

       n	       Number of elements in the vectors.

RETURN VALUES

       Each of the functions returns MLIB_SUCCESS if successful. Otherwise it returns MLIB_FAILURE.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       attributes(5)

SunOS 5.10							    10 Nov 2004 				  mlib_VectorDotProd_U8_Sat(3MLIB)
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