if (xData == null) { 
            throw new IllegalArgumentException("Null 'xData' argument.");
        }
        if (yData == null) { 
            throw new IllegalArgumentException("Null 'yData' argument.");
        }
        if (xData.length != yData.length) {
            throw new IllegalArgumentException(
                "Statistics.getLinearFit(): array lengths must be equal.");