commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/ode/nonstiff/EmbeddedRungeKuttaFieldIntegrator.java [273:292]:
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                for (int k = 1; k < stages; ++k) {

                    for (int j = 0; j < y0.length; ++j) {
                        T sum = yDotK[0][j].multiply(a[k-1][0]);
                        for (int l = 1; l < k; ++l) {
                            sum = sum.add(yDotK[l][j].multiply(a[k-1][l]));
                        }
                        yTmp[j] = y[j].add(getStepSize().multiply(sum));
                    }

                    yDotK[k] = computeDerivatives(getStepStart().getTime().add(getStepSize().multiply(c[k-1])), yTmp);
                }

                // estimate the state at the end of the step
                for (int j = 0; j < y0.length; ++j) {
                    T sum    = yDotK[0][j].multiply(b[0]);
                    for (int l = 1; l < stages; ++l) {
                        sum = sum.add(yDotK[l][j].multiply(b[l]));
                    }
                    yTmp[j] = y[j].add(getStepSize().multiply(sum));
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commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/ode/nonstiff/RungeKuttaFieldIntegrator.java [155:174]:
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            for (int k = 1; k < stages; ++k) {

                for (int j = 0; j < y0.length; ++j) {
                    T sum = yDotK[0][j].multiply(a[k-1][0]);
                    for (int l = 1; l < k; ++l) {
                        sum = sum.add(yDotK[l][j].multiply(a[k-1][l]));
                    }
                    yTmp[j] = y[j].add(getStepSize().multiply(sum));
                }

                yDotK[k] = computeDerivatives(getStepStart().getTime().add(getStepSize().multiply(c[k-1])), yTmp);
            }

            // estimate the state at the end of the step
            for (int j = 0; j < y0.length; ++j) {
                T sum = yDotK[0][j].multiply(b[0]);
                for (int l = 1; l < stages; ++l) {
                    sum = sum.add(yDotK[l][j].multiply(b[l]));
                }
                yTmp[j] = y[j].add(getStepSize().multiply(sum));
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