completed the implementation of the norm

mlx/linalg.cpp

@@ -4,7 +4,7 @@
 #include <numeric>
 #include <set>
 #include <sstream>
-#include <variant>
+#include <string>
 #include <vector>
 
 #include "mlx/array.h"
@@ -14,10 +14,77 @@
 
 namespace mlx::core::linalg {
 
-inline std::vector<int> get_shape_reducing_over_all_dims(int num_axes) {
-  std::vector<int> shape(num_axes);
-  std::iota(shape.begin(), shape.end(), 0);
-  return shape;
+inline array vector_norm(
+    const array& a,
+    const double ord,
+    const std::vector<int>& axis,
+    bool keepdims,
+    StreamOrDevice s) {
+  if (ord == 0.0)
+    return sum(a != 0, axis, keepdims, s);
+  else if (ord == 1.0)
+    return sum(abs(a, s), axis, keepdims, s);
+  else if (ord == 2.0)
+    return sqrt(sum(abs(a, s) * abs(a, s), axis, keepdims, s));
+  else
+    return power(
+        sum(power(abs(a, s), array(ord), s), axis, keepdims, s),
+        array(1.0 / ord));
+}
+
+inline array vector_norm(
+    const array& a,
+    const std::string& ord,
+    const std::vector<int>& axis,
+    bool keepdims,
+    StreamOrDevice s) {
+  if (ord == "inf")
+    return max(abs(a, s), axis, keepdims, s);
+  else if (ord == "-inf")
+    return min(abs(a, s), axis, keepdims, s);
+  std::stringstream error_stream;
+  error_stream << "Invalid ord value " << ord;
+  throw std::invalid_argument(error_stream.str());
+}
+
+inline array matrix_norm(
+    const array& a,
+    const double ord,
+    const std::vector<int>& axis,
+    bool keepdims,
+    StreamOrDevice s) {
+  auto row_axis = axis[0];
+  auto col_axis = axis[1];
+  if (!keepdims && col_axis > row_axis)
+    col_axis -= 1;
+  if (ord == -1.0)
+    return min(sum(abs(a, s), row_axis, keepdims, s), col_axis, keepdims, s);
+  if (ord == 1.0)
+    return max(sum(abs(a, s), row_axis, keepdims, s), col_axis, keepdims, s);
+  if (ord == 2.0 || ord == -2.0)
+    throw std::logic_error("Singular value norms are not implemented.");
+  std::stringstream error_stream;
+  error_stream << "Invalid ord value " << ord << " for matrix norm";
+  throw std::invalid_argument(error_stream.str());
+}
+
+inline array matrix_norm(
+    const array& a,
+    const std::string& ord,
+    const std::vector<int>& axis,
+    bool keepdims,
+    StreamOrDevice s) {
+  if (ord == "f" || ord == "fro")
+    return sqrt(sum(abs(a, s) * abs(a, s), axis, keepdims, s));
+  else if (ord == "inf")
+    return matrix_norm(a, 1.0, {axis[1], axis[0]}, keepdims, s);
+  else if (ord == "-inf")
+    return matrix_norm(a, -1.0, {axis[1], axis[0]}, keepdims, s);
+  if (ord == "nuc")
+    throw std::logic_error("Nuclear norm is not implemented.");
+  std::stringstream error_stream;
+  error_stream << "Invalid ord value " << ord << " for matrix norm";
+  throw std::invalid_argument(error_stream.str());
 }
 
 array norm(
@@ -28,14 +95,65 @@ array norm(
   auto num_axes = axis.size();
 
   if (num_axes == 0 || num_axes == 1 || num_axes == 2)
-    return sqrt(sum(
-        abs(a, s) * abs(a, s),
-        num_axes ? axis : get_shape_reducing_over_all_dims(a.shape().size()),
+    return sqrt(
+        sum(abs(a, s) * abs(a, s),
+            num_axes ? axis
+                     : get_shape_reducing_over_all_axes(a.shape().size()),
             keepdims,
-        s));
+            s),
+        s);
 
   std::stringstream error_stream;
   error_stream << "Invalid axis values " << axis;
   throw std::invalid_argument(error_stream.str());
 }
+
+array norm(
+    const array& a,
+    const double ord,
+    const std::vector<int>& axis,
+    bool keepdims,
+    StreamOrDevice s) {
+  std::vector<int> ax = axis;
+
+  if (axis.empty())
+    ax = get_shape_reducing_over_all_axes(a.ndim());
+  else
+    ax = normalize_axes(ax, a.ndim());
+
+  auto num_axes = ax.size();
+  if (num_axes == 1)
+    return vector_norm(a, ord, ax, keepdims, s);
+  else if (num_axes == 2)
+    return matrix_norm(a, ord, ax, keepdims, s);
+
+  std::stringstream error_stream;
+  error_stream << "Invalid axis values " << ax;
+  throw std::invalid_argument(error_stream.str());
+}
+
+array norm(
+    const array& a,
+    const std::string& ord,
+    const std::vector<int>& axis,
+    bool keepdims,
+    StreamOrDevice s) {
+  std::vector<int> ax = axis;
+
+  if (axis.empty())
+    ax = get_shape_reducing_over_all_axes(a.ndim());
+  else
+    ax = normalize_axes(ax, a.ndim());
+
+  auto num_axes = ax.size();
+  if (num_axes == 1)
+    return vector_norm(a, ord, ax, keepdims, s);
+  else if (num_axes == 2)
+    return matrix_norm(a, ord, ax, keepdims, s);
+
+  std::stringstream error_stream;
+  error_stream << "Invalid axis values " << ax;
+  throw std::invalid_argument(error_stream.str());
+}
+
 } // namespace mlx::core::linalg

mlx/linalg.h

@@ -11,6 +11,18 @@
 #include "string.h"
 
 namespace mlx::core::linalg {
+array norm(
+    const array& a,
+    const double ord,
+    const std::vector<int>& axis = {},
+    bool keepdims = false,
+    StreamOrDevice s = {});
+array norm(
+    const array& a,
+    const std::string& ord,
+    const std::vector<int>& axis = {},
+    bool keepdims = false,
+    StreamOrDevice s = {});
 array norm(
     const array& a,
     const std::vector<int>& axis = {},

mlx/utils.cpp

@@ -1,5 +1,6 @@
 // Copyright © 2023 Apple Inc.
 
+#include <numeric>
 #include <sstream>
 #include <vector>
 
@@ -73,6 +74,12 @@ int normalize_axis(int axis, int ndim) {
   }
   return axis;
 }
+std::vector<int> normalize_axes(const std::vector<int>& axes, int ndim) {
+  std::vector<int> canonical;
+  for (int ax : axes)
+    canonical.push_back(normalize_axis(ax, ndim));
+  return canonical;
+}
 
 std::ostream& operator<<(std::ostream& os, const Device& d) {
   os << "Device(";
@@ -279,4 +286,10 @@ std::ostream& operator<<(std::ostream& os, const std::vector<size_t>& v) {
   return os;
 }
 
+std::vector<int> get_shape_reducing_over_all_axes(int ndim) {
+  std::vector<int> shape(ndim);
+  std::iota(shape.begin(), shape.end(), 0);
+  return shape;
+}
+
 } // namespace mlx::core

mlx/utils.h

@@ -24,6 +24,7 @@ bool is_same_shape(const std::vector<array>& arrays);
  * https://numpy.org/devdocs/reference/generated/numpy.lib.array_utils.normalize_axis_index.html
  */
 int normalize_axis(int axis, int ndim);
+std::vector<int> normalize_axes(const std::vector<int>& axes, int ndim);
 
 std::ostream& operator<<(std::ostream& os, const Device& d);
 std::ostream& operator<<(std::ostream& os, const Stream& s);
@@ -41,4 +42,8 @@ inline std::ostream& operator<<(std::ostream& os, const float16_t& v) {
 inline std::ostream& operator<<(std::ostream& os, const bfloat16_t& v) {
   return os << static_cast<float>(v);
 }
+/**
+ * Returns the axes vector  [0, 1, ... ndim).
+ */
+std::vector<int> get_shape_reducing_over_all_axes(int ndim);
 } // namespace mlx::core