10.shultz_pg48-63

10.shultz_pg48-63 - Pg 48-63 Constructive Lea rning/Cascade...

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Pg 48-63 – Constructive Learning/Cascade Correlation Cascade problem fixes many problems apparent in BP – it was invented to solve 2 problems – learning speed an ability to learn difficulty problems that BP could not solve Curvature and step-size problem CC deals with step size problem in weight adjustment by using information on curvature and slope or the error surface. Slope is rate of change of error with respect to weight Curvature taken as ratio of difference in slope of two points to change in weight of two points Use of this deals with step size problem, ensuring that weight changes in cc can be larger and moe decisive, leading to faster learning than standard BP Unit recruitment and the moving target problem Another difficulty with learning speed is the moving target problem – tendency for hidden units to all run off in the same direction at once (herd effect) before finding their useful role in learning the reduce error Solution is to allow only one hidden unit to evolve at a time – done by starting with 0 hidden units and then recruiting only one hidden unit at a time, as needed to reduce network error
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This note was uploaded on 02/14/2011 for the course PSYC 532 taught by Professor Shultz during the Fall '10 term at McGill.

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10.shultz_pg48-63 - Pg 48-63 Constructive Lea rning/Cascade...

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