Sets the expression of the base alpha spending function as a string. This function is only used if one needs to display the base alpha spending function as a string. This function DOES NOT update the base alpha spending function. One can use setBaseAlphaspendf() to change the base alpha spending function. The spending functions and their string expressions should be defined only once per object. They should not be updated during any interim update to the design.
setAlphaspendfString(theObject, string0)an object of class "sequential.design"
The sequential design object
The string of the expression of the base alpha spending function. Its argument need to be 't'.
design1<-sequential.design()
design1<-setAlphaspendfString(design1,'0.025*t^4')
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