@FUNCTION=interpolation
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@SYNTAX=interpolation(abscissas,ordinates,targets[,interpolation])
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@DESCRIPTION=
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interpolation returns interpolated values corresponding
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to the given abscissa targets as a one column matrix.
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@abscissas are the absicssas of the data to interpolate.
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@ordinates are the ordinates of the data to interpolate.
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* Strings and empty cells in @abscissas and @ordinates are simply ignored.
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@targets are the abscissas of the interpolated data. If several data
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are provided, they must be in the same column, in consecutive cells
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@interpolation is the method to be used for the interpolation;
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possible values are:
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- 0: linear;
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- 1: linear with averaging;
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- 2: staircase;
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- 3: staircase with averaging;
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- 4: natural cubic spline;
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- 5: natural cubic spline with averaging.
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If an averaging method is used, the number of returned values
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is one less than the number of targets since the evaluation is made by
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averaging the interpolation over the interval between two consecutive data;
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in that case, the targets values must be given in increasing order.