sim_Harvard_tracing: Simulate Harvard Spirometer Tracing
In Lightbridge-KS/rslab: Functions for Respiratory System Physiology Lab

This function simulates volume-time tracing data produced by breathing of a hypothetical subject as recorded by the Harvard spirometer. A number of parameters can be specified to adjust the tracing data. The output of this function is a data frame to be plotted by the user.

sim_Harvard_tracing(
  f = "cos",
  t_start = 0,
  t_end = 1,
  paper_speed = 25,
  TV = 500,
  RR = 20,
  oxycons = 0,
  oxycons_unit = c("L/hr", "ml/min"),
  y_int_O2_line = 0,
  seq_x_by = 0.05,
  epsilon_sd = NULL,
  seed = 1
)

`f`	(Character or Symbol) A function to generate 1 respiratory cycle (i.e., inspiration and expiration). The default, currently, is a cosine function. Any function can be specified such that the amplitude is 1 (peak at 1, trough at -1) and the wavelength is `2*pi`.
`t_start`	(Numeric) Time point (minute) when the experiment start
`t_end`	(Numeric) Time point (minute) when the experiment end
`paper_speed`	(Numeric) Paper speed (mm/minute) of the tracing
`TV`	(Numeric) Tidal volume (mL) that subject breath
`RR`	(Numeric) Respiratory Rate (/min) of subject
`oxycons`	(Numeric) Oxygen consumption of subject
`oxycons_unit`	(Character) Units of the `oxycons` must be one of: "L/hr" or "ml/min".
`y_int_O2_line`	(Numeric) Y-intercept of an oxygen-line, i.e., the baseline that passed through the trough of each respiratory cycle waves.
`seq_x_by`	(Numeric) Difference between consecutive `x` values to generate. (similar to `by` argument of `seq()`)
`epsilon_sd`	If provided as numeric, it is a standard deviation of an error term sampled from Gaussian distribution with `mean = 0`
`seed`	(Numeric) If provided `epsilon_sd`, It is a seed to generated random error variation.