plot_constraint-Primers-method: Histogram of Constraint Values.
In openPrimeR: Multiplex PCR Primer Design and Analysis

Plots a histogram of constraint values.

1 2	## S4 method for signature 'Primers' plot_constraint(primers, settings, active.constraints)

`primers`	An evaluated object of class `Primers`.
`settings`	A `DesignSettings` object containing the settings for the constraints to be plotted.
`active.constraints`	Identifiers of constraints to be plotted. provided settings are used to visualize the desired ranges of constraints. If `active.constraints` is not provided, the plotting method will automatically try to plot all constraints defined in `settings`.