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Old 03-04-2007, 08:16 PM   #1
Lain

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Java inverse matrix?
Hello i need to get the inverse matrix for a 3x3 3x3 4x4 and 5x5 matrix's can you guys help me? (i need in java)
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Old 03-04-2007, 09:12 PM   #2
phreak
Re: Java inverse matrix?
Matrices are hard to invert, generally.
I would suggest implementing something like Gaussian Elimination, which is illustarted for finding inverses here.

There is also the LU decomposition method, which is supposedly the most used method for computers, but I don't understand it. I haven't studied matrices other than random glimpses in books from time to time, so don't trust me too much.
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Old 03-05-2007, 05:00 AM   #3
theHunted
Re: Java inverse matrix?
Inverting 3x3 matrices can still be done by hand (see http://mathworld.wolfram.com/MatrixInverse.html).
Everything higher than that has to be done as mentioned by phreak.
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Old 10-14-2009, 11:20 PM   #4
joze_grilj
Ted Re: Java inverse matrix?
Hay, here is my java method for calculating inverse matrix with Gauss-Jordan Method:
Code:
	public double[][] inverz_matrike(double[][]in){
		int st_vrs=in.length, st_stolp=in[0].length;
		double[][]out=new double[st_vrs][st_stolp];
		double[][]old=new double[st_vrs][st_stolp*2];
		double[][]new=new double[st_vrs][st_stolp*2];

		
		for (int v=0;v<st_vrs;v++){//ones vector
			for (int s=0;s<st_stolp*2;s++){
				if (s-v==st_vrs) 
					old[v][s]=1;
				if(s<st_stolp)
					old[v][s]=in[v][s];
			}
		}
		//zeros below the diagonal
		for (int v=0;v<st_vrs;v++){
			for (int v1=0;v1<st_vrs;v1++){
				for (int s=0;s<st_stolp*2;s++){
					if (v==v1)
						new[v][s]=old[v][s]/old[v][v];
					else
						new[v1][s]=old[v1][s];
				}
			}
			old=prepisi(new);		
			for (int v1=v+1;v1<st_vrs;v1++){
				for (int s=0;s<st_stolp*2;s++){
					new[v1][s]=old[v1][s]-old[v][s]*old[v1][v];
				}
			}
			old=prepisi(new);
		}
		//zeros above the diagonal
		for (int s=st_stolp-1;s>0;s--){
			for (int v=s-1;v>=0;v--){
				for (int s1=0;s1<st_stolp*2;s1++){
					new[v][s1]=old[v][s1]-old[s][s1]*old[v][s];
				}
			}
			old=prepisi(new);
		}
		for (int v=0;v<st_vrs;v++){//rigt part of matrix is invers
			for (int s=st_stolp;s<st_stolp*2;s++){
				out[v][s-st_stolp]=new[v][s];
			}
		}
		return out;
	}

	public double[][] prepisi(double[][]in){
		double[][]out=new double[in.length][in[0].length];
		for(int v=0;v<in.length;v++){
			for (int s=0;s<in[0].length;s++){
				out[v][s]=in[v][s];
			}
		}
		return out;
	}
http://nptel.iitm.ac.in/courses/Webc...-2/node27.html
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Old 10-15-2009, 03:31 PM   #5
Feared
 
Re: Java inverse matrix?
Quote:
Originally Posted by joze_grilj View Post
Hay, here is my java method for calculating inverse matrix with Gauss-Jordan Method:
Code:
	public double[][] inverz_matrike(double[][]in){
		int st_vrs=in.length, st_stolp=in[0].length;
		double[][]out=new double[st_vrs][st_stolp];
		double[][]old=new double[st_vrs][st_stolp*2];
		double[][]new=new double[st_vrs][st_stolp*2];

		
		for (int v=0;v<st_vrs;v++){//ones vector
			for (int s=0;s<st_stolp*2;s++){
				if (s-v==st_vrs) 
					old[v][s]=1;
				if(s<st_stolp)
					old[v][s]=in[v][s];
			}
		}
		//zeros below the diagonal
		for (int v=0;v<st_vrs;v++){
			for (int v1=0;v1<st_vrs;v1++){
				for (int s=0;s<st_stolp*2;s++){
					if (v==v1)
						new[v][s]=old[v][s]/old[v][v];
					else
						new[v1][s]=old[v1][s];
				}
			}
			old=prepisi(new);		
			for (int v1=v+1;v1<st_vrs;v1++){
				for (int s=0;s<st_stolp*2;s++){
					new[v1][s]=old[v1][s]-old[v][s]*old[v1][v];
				}
			}
			old=prepisi(new);
		}
		//zeros above the diagonal
		for (int s=st_stolp-1;s>0;s--){
			for (int v=s-1;v>=0;v--){
				for (int s1=0;s1<st_stolp*2;s1++){
					new[v][s1]=old[v][s1]-old[s][s1]*old[v][s];
				}
			}
			old=prepisi(new);
		}
		for (int v=0;v<st_vrs;v++){//rigt part of matrix is invers
			for (int s=st_stolp;s<st_stolp*2;s++){
				out[v][s-st_stolp]=new[v][s];
			}
		}
		return out;
	}

	public double[][] prepisi(double[][]in){
		double[][]out=new double[in.length][in[0].length];
		for(int v=0;v<in.length;v++){
			for (int s=0;s<in[0].length;s++){
				out[v][s]=in[v][s];
			}
		}
		return out;
	}
http://nptel.iitm.ac.in/courses/Webc...-2/node27.html
You do realize that this thread is from 2007?
If so then cool, I'm not a fan of Java though.

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