# t-axis

Home > Settings Menu > t-axis

To change the t-axis limits select this from Settings when on the Function tab. This will produce the "Axis limits" window displaying the current minimum and maximum values for t. Enter new values and select OK. When the t limits are changed the function is resampled and re-displayed, using tmin <=t< tmax and the y-axis limits are reset to encompass the full range of values of y.

Widening the t-axis limits will result in there being more points in the discrete function defined. plotXpose will be slower when performing calculations or drawing graphs with a larger number of points. The maximum number of points that plotXpose will allow in the discrete function definition is 4 096. The number of points is determined by the t-range and the Sampling Interval.

If you want to calculate the Frequency spectrum of a Periodic Function then make sure that the axis limits are such that they include a complete number of periods of the function. For instance cos(pi*t) has a fundamental period of 2. As long as we define the function over a complete number of cycles then we should get a correct representation of the Frequency spectrum of the original sampled periodic function. For cos(pi*t) we could choose, for the minimum and maximum t values, (0,2), (-0.25, 1.75), (-4,0), (-6.2, 3.8), all of which encompass a complete number of cycles so should give approximately the same result after taking the fourier transform to analyse the frequency spectrum, i.e. amplitude 1 and phase 0 at a frequency of 2 with 0 amplitude elsewhere. (Try these limits using a sampling interval of 0.05, and notice that increasing the range for t reduces the frequency sampling interval.)

When defining the values for t you are defining the domain for the function. If there are values of t included within the limits you have defined, for which the function expression cannot be evaluated, then you have defined a relation as there are Undefined Values If there are undefined values then plotXpose will not calculate the derivative, the integral or the Frequency spectrum although the exact derivative will be determined at the sample points where possible.

The t-axis limits cannot be changed for User-Defined Function.

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