Add C API interface

.gitignore

@@ -1,4 +1,3 @@
-
 # Prerequisites
 *.d
 
@@ -58,3 +57,4 @@ dkms.conf
 # ignored files
 build/*
 test/*
+/.vscode

Makefile

@@ -16,6 +16,7 @@ NVCCFLAGS = -I. -I$(CUDA_HOME)/include -O3 -g -gencode arch=compute_90,code=sm_9
 # LDFLAGS for the linker
 LDFLAGS = -L$(CONDA_PREFIX)/lib -L$(CUDA_HOME)/lib64 -lcudart -lcusparse -lcublas -lz -lm
 
+# Source discovery (exclude the debug main)
 C_SOURCES = $(filter-out $(SRC_DIR)/cupdlpx.c, $(wildcard $(SRC_DIR)/*.c))
 CU_SOURCES = $(wildcard $(SRC_DIR)/*.cu)
 
@@ -25,22 +26,41 @@ OBJECTS = $(C_OBJECTS) $(CU_OBJECTS)
 
 TARGET_LIB = $(BUILD_DIR)/libcupdlpx.a
 
+# Debug executable (optional)
 DEBUG_SRC = $(SRC_DIR)/cupdlpx.c
 DEBUG_EXEC = $(BUILD_DIR)/cupdlpx
 
-.PHONY: all clean build
+# Tests auto-discovery
+TEST_DIR := ./test
+TEST_BUILD_DIR := $(BUILD_DIR)/tests
 
+TEST_CU_SOURCES := $(wildcard $(TEST_DIR)/*.cu)
+TEST_C_SOURCES := $(wildcard $(TEST_DIR)/*.c)
+
+# Each test source becomes an executable at build/tests/<basename>
+TEST_EXEC_CU := $(patsubst $(TEST_DIR)/%.cu,$(TEST_BUILD_DIR)/%,$(TEST_CU_SOURCES))
+TEST_EXEC_C := $(patsubst $(TEST_DIR)/%.c,$(TEST_BUILD_DIR)/%,$(TEST_C_SOURCES))
+
+# Phony targets
+.PHONY: all clean build tests test run-tests run-test clean-tests
+
+# Default: build the static library
 all: $(TARGET_LIB)
 
+# Archive all objects into the static library
 $(TARGET_LIB): $(OBJECTS)
 	@echo "Archiving objects into $(TARGET_LIB)..."
+	@mkdir -p $(BUILD_DIR)
 	@ar rcs $@ $^
 
+# Build the debug executable (links the library with cupdlpx.c main)
 build: $(DEBUG_EXEC)
+
 $(DEBUG_EXEC): $(DEBUG_SRC) $(TARGET_LIB)
 	@echo "Building debug executable..."
 	@$(LINKER) $(NVCCFLAGS) $(DEBUG_SRC) -o $(DEBUG_EXEC) $(TARGET_LIB) $(LDFLAGS)
 
+# Pattern rules for objects
 $(BUILD_DIR)/%.o: $(SRC_DIR)/%.c
 	@mkdir -p $(BUILD_DIR)
 	@echo "Compiling $< -> $@..."
@@ -51,6 +71,55 @@ $(BUILD_DIR)/%.o: $(SRC_DIR)/%.cu
 	@echo "Compiling $< -> $@..."
 	@$(NVCC) $(NVCCFLAGS) -c $< -o $@
 
+# Build all tests discovered under test/
+test: tests
+tests: $(TARGET_LIB) $(TEST_EXEC_CU) $(TEST_EXEC_C)
+	@echo "All tests built under $(TEST_BUILD_DIR)/"
+
+# Run all tests one by one
+run-tests: tests
+	@echo "Running all tests..."
+	@set -e; \
+	for t in $(TEST_EXEC_CU) $(TEST_EXEC_C); do \
+	  echo "=== $$t ==="; \
+	  "$$t" || exit $$?; \
+	  echo; \
+	done
+
+# Run a single test by basename: make run-test name=<basename>
+run-test: tests
+	@if [ -z "$(name)" ]; then \
+	  echo "Usage: make run-test name=<basename-of-test-file>"; exit 2; \
+	fi
+	@if [ -x "$(TEST_BUILD_DIR)/$(name)" ]; then \
+	  echo "=== $(TEST_BUILD_DIR)/$(name) ==="; \
+	  "$(TEST_BUILD_DIR)/$(name)"; \
+	else \
+	  echo "Executable not found: $(TEST_BUILD_DIR)/$(name)"; \
+	  echo "Did you 'make tests' and is there a test source named '$(TEST_DIR)/$(name).c(u)'?"; \
+	  exit 1; \
+	fi
+
+# Build rule for CUDA tests: compile and link directly with nvcc
+$(TEST_BUILD_DIR)/%: $(TEST_DIR)/%.cu $(TARGET_LIB)
+	@mkdir -p $(TEST_BUILD_DIR)
+	@echo "Building CUDA test $< -> $@..."
+	@$(LINKER) $(NVCCFLAGS) -I$(SRC_DIR) $< -o $@ $(TARGET_LIB) $(LDFLAGS)
+
+# Build rule for C tests: compile with gcc, link with nvcc to get CUDA libs
+$(TEST_BUILD_DIR)/%: $(TEST_DIR)/%.c $(TARGET_LIB)
+	@mkdir -p $(TEST_BUILD_DIR)
+	@echo "Building C test $< -> $@..."
+	@$(CC) $(CFLAGS) -I$(SRC_DIR) -c $< -o $(TEST_BUILD_DIR)/$*.o
+	@$(LINKER) $(NVCCFLAGS) $(TEST_BUILD_DIR)/$*.o -o $@ $(TARGET_LIB) $(LDFLAGS)
+
+
+# Cleaning
+clean-tests:
+	@echo "Cleaning test executables..."
+	@rm -rf $(TEST_BUILD_DIR)
+
 clean:
 	@echo "Cleaning up..."
-	@rm -rf $(BUILD_DIR) $(TARGET_LIB) $(DEBUG_EXEC)
+	@rm -rf $(BUILD_DIR) $(TARGET_LIB) $(DEBUG_EXEC)
+	@rm -rf $(TEST_BUILD_DIR)

README.md

@@ -71,6 +71,96 @@ The solver generates three text files in the specified <output_directory>. The f
 - `INSTANCE_primal_solution.txt`: The primal solution vector.
 - `INSTANCE_dual_solution.txt`: The dual solution vector.
 
+### C API Example
+
+Besides the command-line interface, cuPDLPx also provides a C API (interface.c) for directly solving LPs in memory. This is useful when integrating cuPDLPx into other C/C++ projects or when generating problems programmatically.
+
+#### Functions and Parameters
+
+The C API involves two main functions:
+
+```c
+lp_problem_t* create_lp_problem(
+    const matrix_desc_t* A_desc,       // constraint matrix A
+    const double* objective_c,         // objective vector c (length n)
+    const double* objective_constant,  // scalar objective offset
+    const double* var_lb,              // variable lower bounds (length n)
+    const double* var_ub,              // variable upper bounds (length n)
+    const double* con_lb,              // constraint lower bounds (length m)
+    const double* con_ub               // constraint upper bounds (length m)
+);
+
+cupdlpx_result_t* solve_lp_problem(
+    const lp_problem_t* prob,
+    const pdhg_parameters_t* params    // NULL → use default parameters
+);
+```
+
+`create_lp_problem` parameters:
+- `A_desc`: Matrix descriptor. Supports `matrix_dense`, `matrix_csr`, `matrix_csc`, `matrix_coo`.
+- `objective_c`: Objective vector. If NULL, defaults to all zeros.
+- `objective_constant`: Scalar constant term added to the objective value. If NULL, defaults to 0.0.
+- `var_lb`: Variable lower bounds. If NULL, defaults to all 0.0.
+- `var_ub`: Variable upper bounds. If NULL, defaults to all +INFINITY.
+- `con_lb`: Constraint lower bounds. If NULL, defaults to all -INFINITY.
+- `con_ub`: Constraint upper bounds. If NULL, defaults to all +INFINITY.
+
+`solve_lp_problem` parameters:
+- `prob`: An LP problem built with `create_LP_problem`.
+- `params`: Solver parameters. If `NULL`, the solver will use default parameters.
+
+#### Example: Solving a Small LP
+```c
+#include "cupdlpx/interface.h"
+#include <math.h>
+#include <stdio.h>
+
+int main() {
+    int m = 3; // number of constraints
+    int n = 2; // number of variables
+
+    // Dense matrix A
+    double A[3][2] = {
+        {1.0, 2.0},
+        {0.0, 1.0},
+        {3.0, 2.0}
+    };
+
+    // Describe A
+    matrix_desc_t A_desc;
+    A_desc.m = m; A_desc.n = n;
+    A_desc.fmt = matrix_dense;
+    A_desc.zero_tolerance = 0.0;
+    A_desc.data.dense.A = &A[0][0];
+
+    // Objective coefficients
+    double c[2] = {1.0, 1.0};
+
+    // Constraint bounds: l <= A x <= u
+    double l[3] = {5.0, -INFINITY, -INFINITY};
+    double u[3] = {5.0, 2.0, 8.0};
+
+    // Build the problem
+    lp_problem_t* prob = create_lp_problem(
+        &A_desc, c, NULL, NULL, NULL, l, u);
+
+    // Solve (NULL → use default parameters)
+    cupdlpx_result_t* res = solve_lp_problem(prob, NULL);
+
+    printf("Termination reason: %d\n", res->termination_reason);
+    printf("Primal objective: %.6f\n", res->primal_objective_value);
+    printf("Dual objective:   %.6f\n", res->dual_objective_value);
+    for (int j = 0; j < res->num_variables; ++j) {
+        printf("x[%d] = %.6f\n", j, res->primal_solution[j]);
+    }
+
+    lp_problem_free(prob);
+    cupdlpx_result_free(res);
+
+    return 0;
+}
+```
+
 ## Reference
 If you use cuPDLPx or the ideas in your work, please cite the source below.
 

build_and_test.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+# ============================
+# cuPDLPx build & test script
+# ============================
+
+# 1. request interactive GPU node
+#echo ">>> Requesting interactive GPU node..."
+#srun --pty --partition=ou_sloan_gpu --cpus-per-task=1 --mem=16G --gres=gpu:1 --time=00:15:00 bash
+
+# 2. load CUDA module
+echo ">>> Loading CUDA module..."
+module purge
+module load cuda/12.4 || { echo "CUDA 12.4 not found, try another version"; exit 1; }
+
+# . show environment info
+which nvcc
+nvcc --version
+echo "CUDA_HOME = $CUDA_HOME"
+
+# 4. build
+echo ">>> Cleaning and building..."
+make clean
+make build
+
+# 5. download test instance if not present
+TESTDIR=$HOME/src/cuPDLPx/test
+mkdir -p $TESTDIR
+if [ ! -f $TESTDIR/2club200v15p5scn.mps.gz ]; then
+    echo ">>> Downloading test instance..."
+    wget -P $TESTDIR https://miplib.zib.de/WebData/instances/2club200v15p5scn.mps.gz
+fi
+
+# 6. run test
+echo ">>> Running smoke test..."
+./build/cupdlpx $TESTDIR/2club200v15p5scn.mps.gz $TESTDIR
+
+echo ">>> Done! Results saved in $TESTDIR"

cupdlpx/cupdlpx.c

@@ -130,31 +130,6 @@ void save_solver_summary(const cupdlpx_result_t *result, const char *output_dir,
     free(file_path);
 }
 
-void set_default_parameters(pdhg_parameters_t *params)
-{
-    params->l_inf_ruiz_iterations = 10;
-    params->has_pock_chambolle_alpha = true;
-    params->pock_chambolle_alpha = 1.0;
-    params->bound_objective_rescaling = true;
-    params->verbose = false;
-    params->termination_evaluation_frequency = 200;
-    params->reflection_coefficient = 1.0;
-
-    params->termination_criteria.eps_optimal_relative = 1e-4;
-    params->termination_criteria.eps_feasible_relative = 1e-4;
-    params->termination_criteria.eps_infeasible = 1e-10;
-    params->termination_criteria.time_sec_limit = 3600.0;
-    params->termination_criteria.iteration_limit = INT32_MAX;
-
-    params->restart_params.artificial_restart_threshold = 0.36;
-    params->restart_params.sufficient_reduction_for_restart = 0.2;
-    params->restart_params.necessary_reduction_for_restart = 0.5;
-    params->restart_params.k_p = 0.99;
-    params->restart_params.k_i = 0.01;
-    params->restart_params.k_d = 0.0;
-    params->restart_params.i_smooth = 0.3;
-}
-
 void print_usage(const char *prog_name)
 {
     fprintf(stderr, "Usage: %s [OPTIONS] <mps_file> <output_dir>\n\n", prog_name);