generalize parallelism to arbitrary num of samples, fix off by one error

examples/more/13_parallelize_min/example.c

@@ -0,0 +1,67 @@
+#include "../../../squiggle.h"
+#include "../../../squiggle_more.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+int main()
+{
+    /* Question: can we parallelize this?
+    A = normal(5,2)
+    B = min(A)
+    B * 20
+    */
+
+    /* Option 1: parallelize taking from n samples */
+    // Question being asked: what is the distribution of sampling 1000 times and taking the min?
+    double sample_min_of_n(uint64_t* seed, int n){
+        double min = sample_normal(5, 2, seed);
+        for(int i=0; i<(n-2); i++){
+            double sample = sample_normal(5, 2, seed);
+            if(sample < min){
+                min = sample;
+            }
+        }
+        return min;
+    }
+    double sampler_min_of_1000(uint64_t* seed) { 
+        return sample_min_of_n(seed, 1000);
+    } 
+
+    int n_samples = 1000000, n_threads = 16;
+    double* results = malloc(n_samples * sizeof(double));
+    parallel_sampler(sampler_min_of_1000, results, n_threads, n_samples);
+    printf("Mean of the distribution of (taking the min of 1000 samples of a normal(5,2)): %f\n", array_mean(results, n_samples));
+    free(results);
+
+    /* Option 2: take the min from n samples cleverly using parallelism */
+    // Question being asked: can we take the min of n samples cleverly?
+    double sample_n_parallel(int n){
+
+        int n_threads = 16;
+        int quotient = n / 16;
+        int remainder = n % 16;
+
+        uint64_t seed = 1000;
+        double result_remainder = sample_min_of_n(&seed, remainder);
+        
+        double sample_min_of_quotient(uint64_t* seed) { 
+            return sample_min_of_n(seed, quotient);
+        }
+        double* results_quotient = malloc(quotient * sizeof(double));
+        parallel_sampler(sample_min_of_quotient, results_quotient, n_threads, quotient);
+
+        double min = results_quotient[0];
+        for(int i=1; i<quotient; i++){
+            if(min > results_quotient[i]){
+                min = results_quotient[i];
+            }
+        }
+        if(min > result_remainder){
+            min = result_remainder;
+        }
+        free(results_quotient);
+        return min;
+    }
+    printf("Minimum of 1M samples of normal(5,2): %f\n", sample_n_parallel(1000000));
+
+}

examples/more/makefile

@@ -48,6 +48,7 @@ all:
 	$(CC) $(OPTIMIZED) $(DEBUG) 10_twitter_thread_example/$(SRC)       $(DEPS) -o 10_twitter_thread_example/$(OUTPUT)
 	$(CC) $(OPTIMIZED) $(DEBUG) 11_billion_lognormals_paralell/$(SRC)  $(DEPS) -o 11_billion_lognormals_paralell/$(OUTPUT)
 	$(CC) $(OPTIMIZED) $(DEBUG) 12_time_to_botec_parallel/$(SRC)       $(DEPS) -o 12_time_to_botec_parallel/$(OUTPUT)
+	$(CC) $(OPTIMIZED) $(DEBUG) 13_parallelize_min/$(SRC)       $(DEPS) -o 13_parallelize_min/$(OUTPUT)
 
 format-all:
 	$(FORMATTER) 00_example_template/$(SRC)
@@ -63,6 +64,7 @@ format-all:
 	$(FORMATTER) 10_twitter_thread_example/$(SRC)
 	$(FORMATTER) 11_billion_lognormals_paralell/$(SRC)
 	$(FORMATTER) 12_time_to_botec_parallel/$(SRC)
+	$(FORMATTER) 13_parallelize_min/$(SRC)
 
 run-all:
 	00_example_template/$(OUTPUT)
@@ -78,6 +80,7 @@ run-all:
 	10_twitter_thread_example/$(OUTPUT)
 	11_billion_lognormals_paralell/$(OUTPUT)
 	12_time_to_botec_parallel/$(OUTPUT)
+	13_parallelize_min/$(OUTPUT)
 
 ## make one DIR=06_nuclear_recovery
 one: $(DIR)/$(SRC)

scratchpad/makefile

@@ -9,7 +9,7 @@ CC=gcc
 # CC=tcc # <= faster compilation
 
 # Main file
-SRC=scratchpad.c ../squiggle.c
+SRC=scratchpad.c ../squiggle.c ../squiggle_more.c
 OUTPUT=scratchpad
 
 ## Dependencies

scratchpad/scratchpad.c

@@ -1,4 +1,5 @@
 #include "../squiggle.h"
+#include "../squiggle_more.h"
 #include <math.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -16,7 +17,18 @@ int main()
 
     }*/
     // Test division
-    printf("\n%d\n", 10 % 3);
+    // printf("\n%d\n", 10 % 3);
+    //
+    
+    int n_samples = 100, n_threads = 16;
+    double* results = malloc(n_samples * sizeof(double));
+    double sampler_scratchpad(uint64_t* seed){
+        return 1;
+    }
+    parallel_sampler(sampler_scratchpad, results, n_threads, n_samples);
+    for(int i=0; i<n_samples; i++){
+        printf("Sample %d: %f\n", i, results[i]);
+    }
 
     free(seed);
 }

squiggle_more.c

@@ -306,10 +306,25 @@ ci convert_lognormal_params_to_ci(lognormal_params y)
 
 /* Parallel sampler */
 void parallel_sampler(double (*sampler)(uint64_t* seed), double* results, int n_threads, int n_samples){
-    if((n_samples % n_threads) != 0){
-        fprintf(stderr, "Number of samples isn't divisible by number of threads, aborting\n");
-        exit(1);
-    }
+    
+    // Division terminology:
+    // a =  b * quotient + reminder
+    // a = (a/b)*b + (a%b)
+    // dividend: a
+    // divisor: b
+    // quotient = a / b
+    // reminder = a % b
+    // "divisor's multiple" := (a/b)*b
+
+    // now, we have n_samples and n_threads
+    // to make our life easy, each thread will have a number of samples of: a/b (quotient)
+    // and we'll compute the remainder of samples separately
+    // to possibly do by Jorge: improve so that the remainder is included in the threads
+
+    int quotient = n_samples / n_threads;
+    int remainder = n_samples % n_threads;
+    int divisor_multiple = quotient * n_threads; 
+
     uint64_t** seeds = malloc(n_threads * sizeof(uint64_t*));
     for (uint64_t i = 0; i < n_threads; i++) {
         seeds[i] = malloc(sizeof(uint64_t));
@@ -321,14 +336,18 @@ void parallel_sampler(double (*sampler)(uint64_t* seed), double* results, int n_
     {
         #pragma omp for
         for (i = 0; i < n_threads; i++) {
-            int lower_bound = i * (n_samples / n_threads);
-            int upper_bound = ((i+1) * (n_samples / n_threads)) - 1;
+            int lower_bound_inclusive = i * quotient;
+            int upper_bound_not_inclusive = ((i+1) * quotient); // note the < in the for loop below, 
             // printf("Lower bound: %d, upper bound: %d\n", lower_bound, upper_bound);
-            for (int j = lower_bound; j < upper_bound; j++) {
+            for (int j = lower_bound_inclusive; j < upper_bound_not_inclusive; j++) {
                 results[j] = sampler(seeds[i]);
             }
         }
     }
+    for(int j=divisor_multiple; j<n_samples; j++){
+        results[j] = sampler(seeds[0]);
+        // we can just reuse a seed, this isn't problematic because we are not doing multithreading
+    }
 
     for (uint64_t i = 0; i < n_threads; i++) {
         free(seeds[i]);