# constraints: Weight constraints In dfalbel/keras: R Interface to 'Keras'

## Description

Functions that impose constraints on weight values.

## Usage

 ```1 2 3 4 5 6 7``` ```constraint_maxnorm(max_value = 2, axis = 0) constraint_nonneg() constraint_unitnorm(axis = 0) constraint_minmaxnorm(min_value = 0, max_value = 1, rate = 1, axis = 0) ```

## Arguments

 `max_value` The maximum norm for the incoming weights. `axis` The axis along which to calculate weight norms. For instance, in a dense layer the weight matrix has shape `input_dim, output_dim`, set `axis` to `0` to constrain each weight vector of length `input_dim,`. In a convolution 2D layer with `dim_ordering="tf"`, the weight tensor has shape `rows, cols, input_depth, output_depth`, set `axis` to `c(0, 1, 2)` to constrain the weights of each filter tensor of size `rows, cols, input_depth`. `min_value` The minimum norm for the incoming weights. `rate` The rate for enforcing the constraint: weights will be rescaled to yield (1 - rate) * norm + rate * norm.clip(low, high). Effectively, this means that rate=1.0 stands for strict enforcement of the constraint, while rate<1.0 means that weights will be rescaled at each step to slowly move towards a value inside the desired interval.

## Details

• `constraint_maxnorm()` constrains the weights incident to each hidden unit to have a norm less than or equal to a desired value.

• `constraint_nonneg()` constraints the weights to be non-negative

• `constraint_unitnorm()` constrains the weights incident to each hidden unit to have unit norm.

• `constraint_minmaxnorm()` constrains the weights incident to each hidden unit to have the norm between a lower bound and an upper bound.

## Custom constraints

You can implement your own constraint functions in R. A custom constraint is an R function that takes weights (`w`) as input and returns modified weights. Note that keras `backend()` tensor functions (e.g. `k_greater_equal()`) should be used in the implementation of custom constraints. For example:

```nonneg_constraint <- function(w) {
w * k_cast(k_greater_equal(w, 0), k_floatx())
}

layer_dense(units = 32, input_shape = c(784),
kernel_constraint = nonneg_constraint)
```

Note that models which use custom constraints cannot be serialized using `save_model_hdf5()`. Rather, the weights of the model should be saved and restored using `save_model_weights_hdf5()`.