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MemoizedFunction

Call memoized function and cache results

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Description

AMemoizedFunctionobject maintains the memoization semantics of a function handle and a cache of the function call results. It has the same calling syntax as the function handle specified in theFunctionproperty. However, theMemoizedFunctionobject is not a function handle.

你第一次调用memoize的函数a certain set of input values, MATLAB®executes the function specified by theFunctionproperty and caches the results. In later calls to the memoized function with the same set of inputs, MATLAB returns the cached results instead of executing the function again.

TheMemoizedFunctionobject maintains the cache of inputs and the corresponding outputs. When it is invoked, MATLAB returns the associated cached output values if the following conditions are true.

  1. The input arguments are numerically equal to cached inputs. When comparing input values, MATLAB treatsNaNs as equal.

  2. The number of requested output arguments matches the number of cached outputs associated with the inputs.

Caution

AMemoizedFunctionobject is not aware of updates to the underlying function. If you modify the function associated with the memoized function, clear the cache with theclearCacheobject function.

Creation

To create aMemoizedFunctionobject, call thememoizefunction.

The memoization of a function is associated with the input function and not with theMemoizedFunctionobject. Therefore, keep the following in mind.

  • Constructing a newMemoizedFunctionobject to the same function creates another reference to the same data. Two variables that memoize the same function share a cache and object property values, such as cache size. In the following example, the variablesaandbshare a cache and have the same value for cache size.

    a = memoize(@svd); b = memoize(@svd);
    Similarly, clearing the cache forb(b.clearCache) also clears the cache fora, and any other variables that memoize thesvdfunction.clearCacheis aMemoizedFunctionobject function.

  • Assigning aMemoizedFunctionobject to a new variable creates another reference to the same data. In the following example, the variablescanddshare data.

    c = memoize(@svd); d = c;

  • Clearing a variable does not clear the cache associated with the input function. To clear the cache for aMemoizedFunctionobject that no longer exists in the workspace, create a newMemoizedFunctionobject to the same function, and use theclearCachefunction on the new object. Alternatively, you can clear caches for allMemoizedFunctionobjects using theclearAllMemoizedCachesfunction.

Properties

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MemoizedFunctionproperties control the behavior of the memoized function. You can access or modify properties of the memoized function. Use dot notation to refer to a particular object and property:

m = memoize(@ones); m.CacheSize = 25;

记忆具有的功能语义应用,回报ned as a function handle. This property is read only.

Data Types:function_handle

Maximum number of cached input and output combinations, specified as a positive integer.

Data Types:double

Caching state, specified astrueorfalse. To instruct MATLAB to call the function specified by theFunctionproperty regardless of whether the results are cached, and not to cache results, set this property tofalse.

Data Types:logical

Object Functions

clearCache Clear cache forMemoizedFunctionobject
stats Return cached values and statistics forMemoizedFunctionobject

Examples

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Open Live Script

Create aMemoizedFunctionobject by memozing thedatetimefunction.

mf = memoize(@datetime)
mf = MemoizedFunction with properties: Function: @datetime Enabled: 1 CacheSize: 10

Change the maximum number of cached input and output combinations.

mf.CacheSize = 2
mf = MemoizedFunction with properties: Function: @datetime Enabled: 1 CacheSize: 2

Call the memoized function with three different input values.

a = mf('today'); b = mf('yesterday'); c = mf('tomorrow');

Call thestatsfunction to investigate the cached results.

s = stats(mf); s.Cache.Inputs{:}
ans =1x1 cell array{'yesterday'}
ans =1x1 cell array{'tomorrow'}

The results of calling the memoized function with'today'are not cached because theCacheSizeis 2.

Open Live Script

In your current working folder, create the following filememoizeSquareExample.mthat contains a function to compute the square of a number. When the function is called, if MATLAB returns cached results,msgis not displayed.

typememoizeSquareExample.m
function m = memoizeSquareExample(n) m = n^2; msg = "The square of " + string(n) + " is " + string(m) +"."; disp(msg) end

Memoize the function. By default, memoization is enabled.

mf = memoize(@memoizeSquareExample);

Call the memoized function twice with the same input value.msgis displayed only once because the second function call returns cached results.

a = mf(42);
The square of 42 is 1764.
b = mf(42);

Disable memoization and call the memoized function with a repeat input value. Although the results for an input of 42 are cached,msgis displayed because memoization is disabled.

mf.Enabled = false; c = mf(42);
The square of 42 is 1764.

Call the memoized function with a different set of inputs.

d = mf(13);
The square of 13 is 169.

Call thestatsfunction to investigate the cached results. MATLAB does not return cached results while memoization is disabled or collect statistics, it continues to store input and output values.

s = mf.stats(); s.Cache.Inputs{:}
ans =1x1 cell array{[42]}

Version History

Introduced in R2017a

See Also

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