CODEWITHSUNDEEP
performanceoptimizationwolfram-mathematica
NUKIL
NUKIL

Reputation: 13

Mathematica optimization append table in a loop

I am kinda of new in Mathematica and there are lots of appendto in my code which I think take up a look of time. I know there are some other ways optimize but I cannot really know exactly how to achieve. I think getBucketShocks can be improved a lot? Anyone?

getBucketShocks[BucketPivots_,BucketShock_,parallelOffset_:0]:=
Module[{shocks,pivotsNb},
shocks={};
pivotsNb=Length[BucketPivots];
If[pivotsNb>1,  
    AppendTo[shocks,LinearFunction[{0,BucketShock},{BucketPivots[[1]],BucketShock},{BucketPivots[[2]],0},BucketPivots[[2]],0},parallelOffset]];

    Do[AppendTo[shocks,LinearFunction[{BucketPivots[[i-1]],0},{BucketPivots[[i]],BucketShock},{BucketPivots[[i+1]],0},{BucketPivots[[i+1]],0},parallelOffset]],{i,2,pivotsNb-1}];

    AppendTo[shocks,LinearFunction[{BucketPivots[[pivotsNb-1]],0},{BucketPivots[[pivotsNb]],BucketShock},{BucketPivots[[pivotsNb]],BucketShock},{BucketPivots[[pivotsNb]],BucketShock},parallelOffset]],    
    If[pivotsNb==1,AppendTo[shocks,BucketShock+parallelOffset&]];
];
shocks];

LinearInterpolation[x_,{x1_,y1_},{x2_,y2_},parallelOffset_:0]:=parallelOffset+y1+(y2-y1)/(x2-x1)*(x-x1);

LinearFunction[p1_,p2_,p3_,p4_,parallelOffset_:0]:=Which[
#<=p1[[1]],parallelOffset+p1[[2]],
#<=p2[[1]],LinearInterpolation[#,p1,p2,parallelOffset],
#<=p3[[1]],LinearInterpolation[#,p2,p3,parallelOffset],
#<=p4[[1]],LinearInterpolation[#,p3,p4,parallelOffset],
#>p4[[1]],parallelOffset+p4[[2]]]&;

Upvotes: 0

Views: 405

Answers (1)

Sjoerd Smit
Sjoerd Smit

Reputation: 186

I think you can optimize the middle Do loop a lot by using some form of Map one way or another. At every iteration, you're trying to access 3 adjacent elements of BucketPivots. This seems like this would be the easiest to do with MovingMap, but you need to jump through a few hoops to get the arguments in the right place. This one is probably the easiest solution:

shocks = MovingMap[
  LinearFunction[
    {#[[1]], 0},
    {#[[2]], BucketShock},
    {#[[3]], 0},
    {#[[3]], 0},
    parallelOffset
  ]&,
  BucketPivots,
  2
]

As a general principle: if you want to do a Do or For loop in Mathematica that runs over the Length of another list, try to find a way you can do it with a function from the Map family (Map, MapIndexed, MapAt, MapThread, etc.) and get familiar with those. They are great substitutions for iterations!

After this, the first and last elements of shocks you can then add with AppendTo.

BTW: here's a free tip. I recommend that in Mathematica you avoid giving variables and functions names that start with a capital (like you did with BucketPivots). All of Mathematica's own symbols start with capitals, so if you avoid starting with them yourself, you'll never clash with a build-in function.

Upvotes: 1

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