Proof of concept C API for Ceres
This introduces a simple C API for a subset of Ceres. This opens the door to
using languages like Python to call Ceres, since it is much easier to bind to C
than it is to bind to C++. It will mean giving up the native Ceres autodiff.
The implementation in this patch does not attempt to do everything but is only
just enough to get started. Subsequent patches will increase the surface area
of Ceres that is covered by the C API.
Change-Id: Ic51804bac6865e1a2e476553248aabc91dff3409
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 94132be..dfe5589 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -43,6 +43,10 @@
ADD_EXECUTABLE(curve_fitting curve_fitting.cc)
TARGET_LINK_LIBRARIES(curve_fitting ceres)
+ADD_EXECUTABLE(curve_fitting_c curve_fitting.c)
+TARGET_LINK_LIBRARIES(curve_fitting_c ceres)
+
+
ADD_EXECUTABLE(robust_curve_fitting robust_curve_fitting.cc)
TARGET_LINK_LIBRARIES(robust_curve_fitting ceres)
diff --git a/examples/curve_fitting.c b/examples/curve_fitting.c
new file mode 100644
index 0000000..fb75d7d
--- /dev/null
+++ b/examples/curve_fitting.c
@@ -0,0 +1,174 @@
+/* Ceres Solver - A fast non-linear least squares minimizer
+ * Copyright 2013 Google Inc. All rights reserved.
+ * http://code.google.com/p/ceres-solver/
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ * - Neither the name of Google Inc. nor the names of its contributors may be
+ * used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Author: mierle@gmail.com (Keir Mierle)
+ *
+ * This is a port of curve_fitting.cc to the minimal C API for Ceres.
+ */
+
+#include <math.h>
+#include <stdio.h>
+#include <string.h> // For NULL
+#include "ceres/c_api.h"
+
+// Data generated using the following octave code.
+// randn('seed', 23497);
+// m = 0.3;
+// c = 0.1;
+// x=[0:0.075:5];
+// y = exp(m * x + c);
+// noise = randn(size(x)) * 0.2;
+// y_observed = y + noise;
+// data = [x', y_observed'];
+
+int num_observations = 67;
+double data[] = {
+ 0.000000e+00, 1.133898e+00,
+ 7.500000e-02, 1.334902e+00,
+ 1.500000e-01, 1.213546e+00,
+ 2.250000e-01, 1.252016e+00,
+ 3.000000e-01, 1.392265e+00,
+ 3.750000e-01, 1.314458e+00,
+ 4.500000e-01, 1.472541e+00,
+ 5.250000e-01, 1.536218e+00,
+ 6.000000e-01, 1.355679e+00,
+ 6.750000e-01, 1.463566e+00,
+ 7.500000e-01, 1.490201e+00,
+ 8.250000e-01, 1.658699e+00,
+ 9.000000e-01, 1.067574e+00,
+ 9.750000e-01, 1.464629e+00,
+ 1.050000e+00, 1.402653e+00,
+ 1.125000e+00, 1.713141e+00,
+ 1.200000e+00, 1.527021e+00,
+ 1.275000e+00, 1.702632e+00,
+ 1.350000e+00, 1.423899e+00,
+ 1.425000e+00, 1.543078e+00,
+ 1.500000e+00, 1.664015e+00,
+ 1.575000e+00, 1.732484e+00,
+ 1.650000e+00, 1.543296e+00,
+ 1.725000e+00, 1.959523e+00,
+ 1.800000e+00, 1.685132e+00,
+ 1.875000e+00, 1.951791e+00,
+ 1.950000e+00, 2.095346e+00,
+ 2.025000e+00, 2.361460e+00,
+ 2.100000e+00, 2.169119e+00,
+ 2.175000e+00, 2.061745e+00,
+ 2.250000e+00, 2.178641e+00,
+ 2.325000e+00, 2.104346e+00,
+ 2.400000e+00, 2.584470e+00,
+ 2.475000e+00, 1.914158e+00,
+ 2.550000e+00, 2.368375e+00,
+ 2.625000e+00, 2.686125e+00,
+ 2.700000e+00, 2.712395e+00,
+ 2.775000e+00, 2.499511e+00,
+ 2.850000e+00, 2.558897e+00,
+ 2.925000e+00, 2.309154e+00,
+ 3.000000e+00, 2.869503e+00,
+ 3.075000e+00, 3.116645e+00,
+ 3.150000e+00, 3.094907e+00,
+ 3.225000e+00, 2.471759e+00,
+ 3.300000e+00, 3.017131e+00,
+ 3.375000e+00, 3.232381e+00,
+ 3.450000e+00, 2.944596e+00,
+ 3.525000e+00, 3.385343e+00,
+ 3.600000e+00, 3.199826e+00,
+ 3.675000e+00, 3.423039e+00,
+ 3.750000e+00, 3.621552e+00,
+ 3.825000e+00, 3.559255e+00,
+ 3.900000e+00, 3.530713e+00,
+ 3.975000e+00, 3.561766e+00,
+ 4.050000e+00, 3.544574e+00,
+ 4.125000e+00, 3.867945e+00,
+ 4.200000e+00, 4.049776e+00,
+ 4.275000e+00, 3.885601e+00,
+ 4.350000e+00, 4.110505e+00,
+ 4.425000e+00, 4.345320e+00,
+ 4.500000e+00, 4.161241e+00,
+ 4.575000e+00, 4.363407e+00,
+ 4.650000e+00, 4.161576e+00,
+ 4.725000e+00, 4.619728e+00,
+ 4.800000e+00, 4.737410e+00,
+ 4.875000e+00, 4.727863e+00,
+ 4.950000e+00, 4.669206e+00,
+};
+
+/* This is the equivalent of a use-defined CostFunction in the C++ Ceres API.
+ * This is passed as a callback to the Ceres C API, which internally converts
+ * the callback into a CostFunction. */
+int exponential_residual(void* user_data,
+ double** parameters,
+ double* residuals,
+ double** jacobians) {
+ double* measurement = (double*) user_data;
+ double x = measurement[0];
+ double y = measurement[1];
+ double m = parameters[0][0];
+ double c = parameters[1][0];
+
+ residuals[0] = y - exp(m * x + c);
+ if (jacobians == NULL) {
+ return 1;
+ }
+ if (jacobians[0] != NULL) {
+ jacobians[0][0] = - m * exp(m * x + c); /* dr/dm */
+ }
+ if (jacobians[1] != NULL) {
+ jacobians[1][0] = - exp(m * x + c); /* dr/dc */
+ }
+ return 1;
+}
+
+int main(int argc, char** argv) {
+ ceres_init(argc, argv);
+
+ /* Note: Typically it is better to compact m and c into one block,
+ * but in this case use separate blocks for illustration. */
+ double m = 0.0;
+ double c = 0.0;
+ double *parameter_pointers[] = { &m, &c };
+ int parameter_sizes[] = { 1, 1 };
+
+ ceres_problem_t* problem = ceres_create_problem();
+ for (int i = 0; i < num_observations; ++i) {
+ ceres_problem_add_residual_block(
+ problem,
+ exponential_residual, /* Cost function */
+ NULL, /* No loss function */
+ &data[2 * i], /* Points to the (x,y) measurement */
+ 1, /* Number of residuals */
+ 2, /* Number of parameter blocks */
+ parameter_sizes,
+ parameter_pointers);
+ }
+
+ ceres_solve(problem);
+
+ printf("Initial m: 0.0, c: 0.0\n");
+ printf("Final m: %g, c: %g\n", m, c);
+ return 0;
+}
