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 * Fluorescence lifetime analysis in SciJava Ops.
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package org.scijava.ops.flim;

import net.imglib2.RandomAccessibleInterval;
import net.imglib2.img.Img;
import net.imglib2.img.array.ArrayImg;
import net.imglib2.img.array.ArrayImgs;
import net.imglib2.img.basictypeaccess.array.FloatArray;
import net.imglib2.loops.LoopBuilder;
import net.imglib2.type.numeric.real.FloatType;
import net.imglib2.view.Views;

/**
 * Ops pertaining to mean lifetime calculation
 *
 * @author Dasong Gao
 * @author Gabriel Selzer
 */
public class MeanLifetimes {

	/**
	 * @param rslt the results from fitting an image
	 * @return the mean lifetime
	 * @implNote op names="flim.tauMean", type=Function
	 */
	public static Img<FloatType> defaultMeanLifetime(FitResults rslt) {
		RandomAccessibleInterval<FloatType> paramMap = rslt.paramMap;
        var nComp = (int) (paramMap.dimension(rslt.ltAxis) - 1) / 2;

        var dim = new long[paramMap.numDimensions() - 1];
		Views.hyperSlice(paramMap, rslt.ltAxis, 0).dimensions(dim);

        var tauM = ArrayImgs.floats(dim);
        var tauASum = ArrayImgs.floats(dim);

		// tauM = sum(a_i * tau_i ^ 2), tauASum = sum(a_j * tau_j)
		for (var c = 0; c < nComp; c++) {
			var A = Views.hyperSlice(rslt.paramMap, rslt.ltAxis, c * 2 + 1);
			var tau = Views.hyperSlice(rslt.paramMap, rslt.ltAxis, c * 2 + 2);
			LoopBuilder.setImages(tau, A, tauM, tauASum) //
				.forEachPixel((t, a, tM, tASum) -> {
                    var f = new FloatType();
					f.set(a);
					f.mul(t);
					tASum.add(f);
					f.mul(t);
					tM.add(f);
				});
		}
        var f = new FloatType();
		f.setReal(Float.MIN_VALUE);
		LoopBuilder.setImages(tauASum, tauM).forEachPixel((tA, tM) -> {
			tA.add(f);
			tM.div(tA);
		});
		return tauM;
	}

}
