* Update sample code for GSL with a more complex example (issue #636)

CHANGELOG.md

@@ -1,4 +1,5 @@
 
+ * Update sample code for GSL with a more complex example ([issue #636](https://github.com/bytedeco/javacpp-presets/issues/636))
  * Fix CUDA build for OpenCV on Mac OS X missing `libopencv_cudev.dylib` ([issue #626](https://github.com/bytedeco/javacpp-presets/issues/626))
  * Upgrade presets for HDF5 1.10.4, Tesseract 4.0.0-rc3, TensorFlow 1.12.0-rc0, and their dependencies
 

gsl/README.md

@@ -19,11 +19,11 @@ Java API documentation is available here:
 
 Sample Usage
 ------------
-Here is a simple example of GSL ported to Java from this C source file:
+Here is a simple example of GSL ported to Java from this demo.c source file:
 
- * https://www.gnu.org/software/gsl/manual/html_node/An-Example-Program.html
+ * https://www.gnu.org/software/gsl/manual/html_node/Random-Number-Distribution-Examples.html
 
-We can use [Maven 3](http://maven.apache.org/) to download and install automatically all the class files as well as the native binaries. To run this sample code, after creating the `pom.xml` and `src/main/java/Example.java` source files below, simply execute on the command line:
+We can use [Maven 3](http://maven.apache.org/) to download and install automatically all the class files as well as the native binaries. To run this sample code, after creating the `pom.xml` and `src/main/java/Demo.java` source files below, simply execute on the command line:
 ```bash
  $ mvn compile exec:java
 ```
@@ -33,10 +33,10 @@ We can use [Maven 3](http://maven.apache.org/) to download and install automatic
 <project>
     <modelVersion>4.0.0</modelVersion>
     <groupId>org.bytedeco.javacpp-presets.gsl</groupId>
-    <artifactId>example</artifactId>
+    <artifactId>demo</artifactId>
     <version>1.4.3</version>
     <properties>
-        <exec.mainClass>Example</exec.mainClass>
+        <exec.mainClass>Demo</exec.mainClass>
     </properties>
     <dependencies>
         <dependency>
@@ -48,16 +48,39 @@ We can use [Maven 3](http://maven.apache.org/) to download and install automatic
 </project>
 ```
 
-### The `src/main/java/Example.java` source file
+### The `src/main/java/Demo.java` source file
 ```java
 import org.bytedeco.javacpp.*;
 import static org.bytedeco.javacpp.gsl.*;
 
-public class Example {
+public class Demo {
     public static void main(String[] args) {
-        double x = 5.0;
-        double y = gsl_sf_bessel_J0(x);
-        System.out.printf("J0(%g) = %.18e\n", x, y);
+        gsl_rng_type T;
+        gsl_rng r;
+
+        int n = 10;
+        double mu = 3.0;
+
+        /* create a generator chosen by the 
+           environment variable GSL_RNG_TYPE */
+
+        gsl_rng_env_setup();
+
+        T = gsl_rng_default();
+        r = gsl_rng_alloc(T);
+
+        /* print n random variates chosen from 
+           the poisson distribution with mean 
+           parameter mu */
+
+        for (int i = 0; i < n; i++) {
+            int k = gsl_ran_poisson(r, mu);
+            System.out.printf(" %d", k);
+        }
+
+        System.out.println();
+        gsl_rng_free(r);
+        System.exit(0);
     }
 }
 ```