## Change substance concentration patterns in the environment according to a gradient

### Description

The generic function createGradient changes specific substance concentration patterns in the environment.

### Usage

createGradient(
object,
mediac,
position,
smax,
steep,
unit = "mmol/cell"
)

## S4 method for signature 'Arena'
object,
mediac,
position,
smax,
steep,
unit = "mmol/cell"
)


### Arguments

 object An object of class Arena. mediac A character vector giving the names of substances, which should be added to the environment (the default takes all possible substances). position A character vector giving the position (top, bottom, right and left) of the gradient. smax A number giving the maximum concentration of the substance. steep A number between 0 and 1 giving the steepness of the gradient (concentration relative to the arena size). add A boolean variable defining whether the amount of substance should be summed or replaced unit A character used as chemical unit to set the amount of the substances to be added (valid values are: mmol/cell, mmol/cm2, mmol/arena, mM)

### Details

This function can be used to add gradients of specific substances in the environment.

Arena-class and changeSub

### Examples

data(Ec_core, envir = environment()) #get Escherichia coli core metabolic model
bac <- Bac(Ec_core,deathrate=0.05,
minweight=0.05,growtype="exponential") #initialize a bacterium
arena <- Arena(n=20,m=20) #initialize the environment