Gradient_descent.gif
Summary
Description Gradient descent.gif |
English:
Gradient descent is a simple method to find the minimum of a function, where at each iteration a small step is made in the direction of the steepest descent. It tends to get stuck in a local minimum, so it is often run with several initial conditions.
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Date | |
Source | https://twitter.com/j_bertolotti/status/1121054414066810881 |
Author | Jacopo Bertolotti |
Permission
( Reusing this file ) |
https://twitter.com/j_bertolotti/status/1030470604418428929 |
Mathematica 11.0 code
f = Evaluate[x^2 + y^2 + Total@Table[RandomReal[{0,2}] E^(-(((x - RandomReal[{-1, 1}])^2 + (y + RandomReal[{-1, 1}])^2)/(2 RandomReal[{0.1, 0.4}]^2))), {10}]]; step = 0.02; nstep = 100; coord = {-1, 1}; pos = {coord[[1]], coord[[2]], f /. {x -> coord[[1]], y -> coord[[2]]}}; evo = Reap[Do[ subst = MapThread[Rule, {{x, y, z}, pos}]; dfx = (D[{x, y, f}, x] /. subst); dfy = (D[{x, y, f}, y] /. subst); tmp = {D[f, x] /. subst, D[f, y] /. subst}; pos = pos - step {tmp[[1]], tmp[[2]], 0}; pos[[3]] = Evaluate[f /. {x -> pos[[1]], y -> pos[[2]]}]; Sow[pos]; , nstep];][[2, 1]]; coord = {-1, -1}; pos = {coord[[1]], coord[[2]], f /. {x -> coord[[1]], y -> coord[[2]]}}; evo1 = Reap[Do[ subst = MapThread[Rule, {{x, y, z}, pos}]; dfx = (D[{x, y, f}, x] /. subst); dfy = (D[{x, y, f}, y] /. subst); tmp = {D[f, x] /. subst, D[f, y] /. subst}; pos = pos - step {tmp[[1]], tmp[[2]], 0}; pos[[3]] = Evaluate[f /. {x -> pos[[1]], y -> pos[[2]]}]; Sow[pos]; , nstep];][[2, 1]]; coord = {1, 1}; pos = {coord[[1]], coord[[2]], f /. {x -> coord[[1]], y -> coord[[2]]}}; evo2 = Reap[Do[ subst = MapThread[Rule, {{x, y, z}, pos}]; dfx = (D[{x, y, f}, x] /. subst); dfy = (D[{x, y, f}, y] /. subst); tmp = {D[f, x] /. subst, D[f, y] /. subst}; pos = pos - step {tmp[[1]], tmp[[2]], 0}; pos[[3]] = Evaluate[f /. {x -> pos[[1]], y -> pos[[2]]}]; Sow[pos]; , nstep];][[2, 1]]; p1 = Table[ Show[ Plot3D[f, {x, -1.35, 1.35}, {y, -1.35, 1.35}, Boxed -> False, Axes -> False(*,PlotStyle\[Rule]{Opacity[0.3]}*)], Graphics3D[{PointSize[0.03], Point[evo[[j]] ], Thick, Line[evo[[1 ;; j]] ], Point[evo1[[j]] ], Line[evo1[[1 ;; j]]] , Point[evo2[[j]] ], Line[evo2[[1 ;; j]]] }] ] , {j, 1, nstep, 2}]; ListAnimate[p1]
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