I am trying to define a binary decision variable in java using cplex. That's a two dimensional variable. It means that if a path starts from a specific station it should be 1 or otherwise 0. I have a set of station, J and a set of paths, K and my decision variable is Z_jk. Currently I am defining the code like following, but it doesn't work. Could anybody please help me?
Thanks in advance.
// define variables
z = new IloNumVar[stations_start.size()][];
for (int j=0; j<stations_start.size();j++) {
z[j] = cplex.numVarArray(paths.size(),0,1);
for (int k=0;k<paths.size();k++) {
z[j][k] = cplex.numVar(new_column, 0, 1,"z");
z[j][k].setName("z."+j+"."+k);
}
}
You are trying to create a 2D array of binary decision variables. What errors are you getting?
Try looking at some of the sample code provided with CPLEX. See for example transport.java which includes some 2D arrays of variables declared and initialised like this:
IloNumVar[][] x = new IloNumVar[nbSupply][];
IloNumVar[][] y = new IloNumVar[nbSupply][];
for (int i = 0; i < nbSupply; i++) {
x[i] = cplex.numVarArray(nbDemand, 0., Double.MAX_VALUE);
y[i] = cplex.numVarArray(nbDemand, 0., Double.MAX_VALUE);
}
For a binary decision variable you may prefer to use IloBoolVar rather than the IloNumVar or even IloIntVar options.
You do need to declare the dimension in one of two ways, however. You've declared new IloNumVar[stations_start.size()][]; but not specified the second dimension. The easiest approach would be to declare:
z = new IloBoolVar[stations_start.size()][paths.size()];
Alternately you can keep your existing declaration, but in the loop add on the second dimension:
z = new IloBoolVar[stations_start.size()][];
for (int j=0; j<stations_start.size(); j++) {
z[j] = new IloBoolVar[paths.size()];
... existing assignments ...
}
Related
I'm working on job shop scheduling problem and i'm using Cplex in Java and want to define a binary decision variable x[i][j][k] with i=(1..n) with n=number of job , j=(1..m) with m=number of operation by job and k=(1..M) with M=number of machine.
And, i want to intialize this these kind of variables
How can i do this?
Without having tested, this snippet should intialize a 3D array of boolean decision variables:
IloCplex cplex = new IloCplex();
IloNumVar[][][] x = new IloNumVar[n][][];
for (int i = 0; i < n; i++){
x[i] = new IloNumVar[m][];
for (int j = 0; j < m; j++){
x[i][j] = cplex.boolVarArray(M);
}
}
Take a look at the CPLEX Java examples. Understanding these simple examples could even take less time than posting your question here.
So I am making a program that needs to be overwrite value i from ArrayList to value i in array. For the life of me I cannot figure out what I should do. I've tried looking for similar problems here, but can't seem to find them. Obviously, my loop is very wrong as it is, as it is just overwriting the entire loop, but I can't figure it out. Any kind-hearted person want to help me?
BTW, I am using Java with Processing
Dot[] dots = new Dot[16];
ArrayList<Dot> extraDots = new ArrayList<Dot>();
Fill them with values and later ...
for (int i = 0; i < dots.length; ++i) {
if (dots[i].timeRemain == 0 && !dotTouch)
{
//arrayCopy(extraDots, i, dots, i, 1);
//this is basically what I want, but from an arraylist to the array
dots = extraDots.toArray(new Dot[i]); //So, so wrong, I know
dotTouch = true;
}
dotTouch = false;
You mean
dots[i] = extraDots.get(i);
???
i didn't get your problem..
simply you can do like below to copy from arraylist to array
why you are using dots[i].timeRemain and dotTouch. can you clarify??
for (int i = 0; i < dots.length; ++i) {
dots[i] = extraDots.get(i);
}
This is one of the first programs I am writing by myself. I want to make a physics calculator where many objects can interact with each other and give the user an option to add more objects. My idea is to have a for loop that runs through each object pulling on each other like this.
for(int n=1; n<=totalObjs; n++){
objName = "object"+n;
for(int i=1; i<n; i++){
obj2Name = "object"+i
objName.getMass();
//getting mass and position from both
//calculations here}
for(int x=n+1; x<=totalObjs; x++){
//same stuff as in the previous for loop}
}
I know there are probably huge syntax errors or logical errors in that but I'd like to sort through those on my own. Is there some way i could reference objects with the strings?
Is there some way i could reference objects with the strings?
Yes, via a Map<String, SomeType> such as a HashMap<String, SomeType>.
Think of this as being similar to an array or ArrayList, but instead of using number indices, you'd be using String indices.
Now looking at your code however, you might be better off using a simple ArrayList or array, since you appear to be trying to use numeric indices.
e.g.,
// assume a class called GravMass which has Mass, position, and momentum
List<GravMass> gravMassList = new ArrayList<GravMass>();
// fill your list
for(int i = 0; i < gravMassList.size() - 1; i++) {
GravMass gravMass1 = gravMassList.get(i);
int mass1 = gravMass1.getMass();
for(int j = i + 1; j < gravMassList.size(); j++){
GravMass gravMass2 = gravMassList.get(j);
int mass2 = gravMass2.getMass();
//getting mass and position from both
//calculations here}
}
}
I'm trying to write a simple game where an enemy chases the player on a grid. I'm using the simple algorithm for pathfinding from the Wikipedia page on pathfinding. This involves creating two lists with each list item containing 3 integers. Here's test code I'm trying out to build and display such a list.
When I run the following code, it prints out the same numbers for each array in the ArrayList. Why does it do this?
public class ListTest {
public static void main(String[] args) {
ArrayList<Integer[]> list = new ArrayList<Integer[]>();
Integer[] point = new Integer[3];
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 3; j++) {
point[j] = (int)(Math.random() * 10);
}
//Doesn't this line add filled Integer[] point to the
//end of ArrayList list?
list.add(point);
//Added this line to confirm that Integer[] point is actually
//being filled with 3 random ints.
System.out.println(point[0] + "," + point[1] + "," + point[2]);
}
System.out.println();
//My current understanding is that this section should step through
//ArrayList list and retrieve each Integer[] point added above. It runs, but only
//the values of the last Integer[] point from above are displayed 10 times.
Iterator it = list.iterator();
while (it.hasNext()) {
point = (Integer[])it.next();
for (int i = 0; i < 3; i++) {
System.out.print(point[i] + ",");
}
System.out.println();
}
}
}
First of all, several of the other answers are misleading and/or incorrect. Note that an array is an object. So you can use them as elements in a list, no matter whether the arrays themselves contain primitive types or object references.
Next, declaring a variable as List<int[]> list is preferred over declaring it as ArrayList<int[]>. This allows you to easily change the List to a LinkedList or some other implementation without breaking the rest of your code because it is guaranteed to use only methods available in the List interface. For more information, you should research "programming to the interface."
Now to answer your real question, which was only added as a comment. Let's look at a few lines of your code:
Integer[] point = new Integer[3];
This line creates an array of Integers, obviously.
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 3; j++) {
point[j] = (int)(Math.random() * 10);
}
//Doesn't this line add filled Integer[] point to the
//end of ArrayList list?
list.add(point);
//...
}
Here you assign values to the elements of the array and then add a reference to the array to your List. Each time the loop iterates, you assign new values to the same array and add another reference to the same array to the List. This means that the List has 10 references to the same array which has been repeatedly written over.
Iterator it = list.iterator();
while (it.hasNext()) {
point = (Integer[])it.next();
for (int i = 0; i < 3; i++) {
System.out.print(point[i] + ",");
}
System.out.println();
}
}
Now this loop prints out the same array 10 times. The values in the array are the last ones set at the end of the previous loop.
To fix the problem, you simply need to be sure to create 10 different arrays.
One last issue: If you declare it as Iterator<Integer[]> it (or Iterator<int[]> it), you do not need to cast the return value of it.next(). In fact this is preferred because it is type-safe.
Finally, I want to ask what the ints in each array represent? You might want to revisit your program design and create a class that holds these three ints, either as an array or as three member variables.
I would highly recommend to enclose the integer array of 3 numbers into a meaningful class, that would hold, display and control an array of 3 integers.
Then in your main, you can have an growing ArrayList of objects of that class.
You have an extra ) here:
element = (int[])it.next()); //with the extra parenthesis the code will not compile
should be:
element = (int[])it.next();
Besides the problem in the other answer, you cal it.next() two times, that cause the iterator move forward two times, obviously that's not what you want. The code like this:
element = (int[])it.next());
String el = (String)element;
But actually, I don't see you used el. Although it's legal, it seems meaningless.
Can you create a line of code, within a while-loop, that will create a new array AND change the array's name with each iteration of the while loop?
Example:
int size = 10;
int name_count = 1;
while(size <= 100)
{
//name_count is changing the name of the array by calling it
// "array1", "array2", etc...
//I know this may not be correct code for changing the name of
// the array, but it is suppose to get the point across.
int[] array(name_count) = new int[size];
for (int i = 0; i <= size; i++)
{ /* Adding numbers to an array */ }
size = size + 5;
name_count++;
}
Identifier names need to be defined at compile time. So you can't explicitly use a different variable name on each iteration of the loop.
Another problem with your pseudo-code is that, if the array were to be declared inside the loop, it would fall out of scope when the loop completes, so there wouldn't be much point.
To do something like this you need to use some collection to hold the arrays, and it would be easier to make them explicit objects instead of just arrays. Something like:
List<List<Integer>> listOfArrays = new ArrayList<List<Integer>>();
while (size <= 100) {
List<Integer> listOfNumbers = new ArrayList<Integer>(size);
/* insert loop here to add numbers to listOfNumber */
size += 5;
name_count += 1;
}
Then you can access each list of numbers using an index into listOfArrays -- equivalent to naming each one with the index, but handled at runtime instead of compile time.
You cannot change the array's name, It will just re-declare the array with each successful loop. (It will be a new blank array.) I think what you are looking for is a two dimensional array.
int[][] myArray = new int[3][3];