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Add option to print loss every printInterval epochs in PrintLoss callback. #442

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Add option to print loss every printInterval epochs in PrintLoss callback. #442

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ada7eda
Add printInterval to PrintLoss Callback
ranjodhsingh1729 Oct 19, 2025
e094b3a
Modify Callback Documentation
ranjodhsingh1729 Oct 19, 2025
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2 changes: 2 additions & 0 deletions doc/callbacks.md
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Original file line number Diff line number Diff line change
Expand Up @@ -249,12 +249,14 @@ Callback that prints loss to stdout or a specified output stream.

* `PrintLoss()`
* `PrintLoss(`_`output`_`)`
* `PrintLoss(`_`output, printInterval`_`)`

#### Attributes

| **type** | **name** | **description** | **default** |
|----------|----------|-----------------|-------------|
| `std::ostream` | **`output`** | Ostream which receives output from this object. | `stdout` |
| `size_t` | **`printInterval`** | The number of epochs between consecutive loss prints. | `1` |

#### Examples:

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20 changes: 16 additions & 4 deletions include/ensmallen_bits/callbacks/print_loss.hpp
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Expand Up @@ -12,6 +12,8 @@
#ifndef ENSMALLEN_CALLBACKS_PRINT_LOSS_HPP
#define ENSMALLEN_CALLBACKS_PRINT_LOSS_HPP

#include <stdexcept>

namespace ens {

/**
Expand All @@ -25,8 +27,14 @@ class PrintLoss
*
* @param ostream Ostream which receives output from this object.
*/
PrintLoss(std::ostream& output = arma::get_cout_stream()) : output(output)
{ /* Nothing to do here. */ }
PrintLoss(std::ostream& output = arma::get_cout_stream(),
const size_t printInterval = 1)
: output(output), printInterval(printInterval)
{
if (printInterval == 0)
throw std::invalid_argument(
"PrintLoss(): printInterval cannot be zero.");
}

/**
* Callback function called at the end of a pass over the data.
Expand All @@ -41,16 +49,20 @@ class PrintLoss
bool EndEpoch(OptimizerType& /* optimizer */,
FunctionType& /* function */,
const MatType& /* coordinates */,
const size_t /* epoch */,
const size_t epoch,
const double objective)
{
output << objective << std::endl;
// epochs are 1-indexed.
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Are they? I thought they started at 0. In either case, it doesn't really make a big difference: if they are 0-indexed they will print the first iteration too.

if (epoch % printInterval == 0)
output << objective << std::endl;
return false;
}

private:
//! The output stream that all data is to be sent to; example: std::cout.
std::ostream& output;
//! The number of epochs between consecutive loss prints.
const size_t printInterval;
};

} // namespace ens
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