err.breakage: Error function for estimated tip geometry

Description

Calculates the residual sum of squares error between measured resistance data and the predicted resistances for a given set of model parameters.

Usage

err.breakage(params, data, rho = 51, l = 1000)

Arguments

params

A vector of the 2 tip geometry parameters, where params[1] is the half-cone angle in radians, and params[2] is the initial inner radius in microns.

data

The recorded data as an XY list or data frame, where data$x contains the breakage distances in microns and data$y holds the corresponding resistances in megohms.

rho

Resistivity of the filler solution, in ohm centimetres. The default value of 51 ohm cm corresponds to a 150 mM solution of KCl.

The initial length of the pipette tip. Because the resistance is dominated by the narrower tip region, the precise value of this is not usually important provided it is much greater than the breakage distance.

Value

Details

This function quantifies the error between a posited model of the pipette tip geometry and the results actually recorded. It is organised for minimisation by the standard optim function, and is used as such within fit.breakage. It is not expected to be much used outside that context.

Examples

Run this code

# estimate breakage data for one geometry
brks <- 0.2 * 0:10
res <- resist.breakage(brks, theta=4*pi/180, r=0.05, rho=64)
dat <- list(x=brks, y=res)

# compare it to different geometry
err.breakage(c(2*pi/180, 0.1), dat, rho=64)
err.breakage(c(6*pi/180, 0.02), dat, rho=64)