... radiation. The extent of the effect of its presence on the radiation spectrum, together with the resolution and signal-to-noise of the instrument, determine the accuracy of the measurement. In the ... minimum is easily found by inverting the matrix corresponding to the forward model. Since the forward model is usually non-linear, some search method has to be applied to find the minimum. For ... non-linear models, the minimum can be found by linearizing the model around some initial estimate and iteratively applying the matrix inversion and re-computing the forward matrix for the new...