Multi task learning in Keras

deep-learningkeraskeras-layermachine learningneural-network

I am trying to implement shared layers in Keras. I do see that Keras has keras.layers.concatenate, but I am unsure from documentation about its use. Can I use it to create multiple shared layers? What would be the best way to implement a simple shared neural network as shown below using Keras?

Edit 1:
Note that all the shape of input, output and shared layers for all 3 NNs are the same. There are multiple shared layers (and non-shared layers) in the three NNs. The coloured layers are unique to each NN, and have same shape.

Basically, the figure represents 3 identical NNs with multiple shared hidden layers, followed by multiple non-shared hidden layers.

I am unsure how to share multiple layers as in the Twitter example, there was just one shared layer (example in API doc).

Edit 2:
Based on geompalik's helpful comments, this is what I initially came up with:

sharedLSTM1 = LSTM((data.shape[1]), return_sequences=True)
sharedLSTM2 = LSTM(data.shape[1])
def createModel(dropoutRate=0.0, numNeurons=40, optimizer='adam'):
    inputLayer = Input(shape=(timesteps, data.shape[1]))
    sharedLSTM1Instance = sharedLSTM1(inputLayer)
    sharedLSTM2Instance =  sharedLSTM2(sharedLSTM1Instance)
    dropoutLayer = Dropout(dropoutRate)(sharedLSTM2Instance)
    denseLayer1 = Dense(numNeurons)(dropoutLayer)
    denseLayer2 = Dense(numNeurons)(denseLayer1)
    outputLayer = Dense(1, activation='sigmoid')(denseLayer2)
    return (inputLayer, outputLayer)

inputLayer1, outputLayer1 = createModel()
inputLayer2, outputLayer2 = createModel()
model = Model(inputs=[inputLayer1, inputLayer2], outputs=[outputLayer1, outputLayer2])
model.compile(loss='binary_crossentropy', optimizer='adam', metrics=['accuracy'])

In the above code, I expect that the LSTM Layers in the two models are shared, whereas the dropout and 2 dense layers are not shared. Is that correct?

If so, I do not need keras.layers.concatenate in this example, right?

I get the following image if I try to visualise the network using plot_model (which is what I was expecting):

Best Answer

Implementing the shown architecture is quite straight-forward with the functional API of Keras. Check this page for more information on that.

In your case you have the input layer and the first hidden layer shared, and then one layer for each of the three subjects. Designing your model is now a matter of how your data look: for instance, if for a given input you have different outputs for each subject, you can should define a model like:

model = Model(inputs=[you_main_input], outputs=[subject1_output, subject2_output, subject3_output])

If that is not the case, and you have training data corresponding to each of the subjects, you can define three NNs, and have the first two layers shared across them. Check under "Shared layers" in the above-cited documentation.

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Android – How to create layout with 6 buttons like windows tiles

I'd use a vertical LinearLayout with three rows of same weight as children, each row being a horizontal LinearLayout having two children of same weights, which will make sure the full area is filled. For six buttons performance shouldn't be an issue.

If performance is a concern, you can make the rows as RelativeLayouts and use a strut to split in half and position the two children based on that.

When I say a strut, I mean this:

<View android:id="@+id/strut"
    android:layout_width="0dp"
    android:layout_height="0dp" 
    android:layout_centerHorizontal="true"/>

Update: Since you're trying the LinearLayouts, here's how you can deal with the heights and widths:

The parent LinearLayout can have:

android:layout_width="match_parent"
android:layout_height="match_parent"

The three LinearLayout children will have:

android:layout_width="match_parent"
android:layout_height="0dip"

The Buttons will have:

android:layout_width="0dip"
android:layout_height="match_parent"

As you can notice, we have 0dip for the property that weight is applied on (either on height if parent is vertical oriented, or width if parent is horizontal oriented), which will need to grow to fill in the space.

Here's the full XML (buttons don't include drawables, so feel free to add yours):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dip"
        android:orientation="horizontal"
        android:layout_weight="1" >

        <Button
            android:layout_width="0dip"
            android:layout_height="match_parent"
            android:layout_weight="1" />

        <Button
            android:layout_width="0dip"
            android:layout_height="match_parent"
            android:layout_weight="1"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dip"
        android:orientation="horizontal"
        android:layout_weight="1" >

        <Button
            android:layout_width="0dip"
            android:layout_height="match_parent"
            android:layout_weight="1" />

        <Button
            android:layout_width="0dip"
            android:layout_height="match_parent"
            android:layout_weight="1"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dip"
        android:orientation="horizontal"
        android:layout_weight="1" >

        <Button
            android:layout_width="0dip"
            android:layout_height="match_parent"
            android:layout_weight="1" />

        <Button
            android:layout_width="0dip"
            android:layout_height="match_parent"
            android:layout_weight="1" />
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</LinearLayout>

And the result: enter image description here

Angularjs – JSDoc with AngularJS

I have encountered this issue as well. I am now writing documentation for angularjs codes through jsdoc comments like this:

1.Make a blank .js file with the following comment:

 /**
  * @namespace angular_module
  */

This will create a separate html in the generated documentation for listing all modules.

2.In javascript files that defines any new angular module, use this kind of comment

 /**
  * @class angular_module.MyModule
  * @memberOf angular_module    
  */

This will add an item in the above listing of all angular_modules, as well as creating a separate html page for MyModule, because it is a class.

3.For each angularjs service, use the following comment:

 /**
  * @function myService
  * @memberOf angular_module.MyModule
  * @description This is an angularjs service.
  */

This will add an item in the MyModule page for the service. Because it is added as a function, you can write documentation for input parameters using '@param' and return values using '@return'.

4.If I have quite long codes in a controller or directive of MyModule and want to have a separate html file to document it, I will annotate the controller or directive as a class using full path. e.g.

 /**
  * @class angular_module.MyModule.MyController
  */

In this way, MyController will be listed as one item in MyModule's documentation page.

Then, we can annotate codes within the controller as member functions of MyController.

 /**
  * @name $scope.aScopeFunction
  * @function
  * @memberOf angular_module.MyModule.MyController
  * @description
  */

In this way, this function's documentation will appear in the html file of MyController's html page. The dot-separated full path string builds the connection.

There are three types of syntaxes for namepath:

Person#say // the instance method named "say."
Person.say // the static method named "say."
Person~say // the inner method named "say."

However, one imperfect point of commenting controller as a class is that a "new" will be found before the controller name in the generated html documentation because it is described as class constructor.

Furthermore, you can define namespaces in order to add a hierarchical structure. For example, you can define a namespace to include all controllers
```
/**
 * @namespace MyApp.Controllers
 */
```

, and prefix all controller with MyApp.Controllers. You can also define namespaces like MyApp.Product or MyApp.Customer etc.

Although not perfect, I like using jsdoc to document angularjs codes because

It is simple;
The module-controller-function hierarchy are kept;
And it keeps jsdoc's merit that it is a browsable documentation site.

A table style jsdoc stylesheet:

Particularly, I've adapted the default jsdoc stylesheet to a table style like the Java API documentation. It looks clearer.

In Windows, I replace this file: C:\Users\user1\AppData\Roaming\npm\node_modules\jsdoc\templates\default\static\styles with this file https://github.com/gm2008/jsdoc/blob/master/templates/default/static/styles/jsdoc-default.css

That's it.

Best Answer

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Angularjs – JSDoc with AngularJS

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