e04ab {NAGFWrappers}  R Documentation 
e04ab searches for a minimum, in a given finite interval, of a continuous function of a single variable, using function values only. The method (based on quadratic interpolation) is intended for functions which have a continuous first derivative (although it will usually work if the derivative has occasional discontinuities).
e04ab(funct, e1, e2, a, b, maxcal)
funct 
function You must supply this function to calculate the value of the function F(x) at any point x in [ab]. It should be tested separately before being used in conjunction with e04ab.

e1 
double The relative accuracy to which the position of a minimum is required. (Note that, since e1 is a relative tolerance, the scaling of x is automatically taken into account.) 
e2 
double The absolute accuracy to which the position of a minimum is required. e2 should be no smaller than 2ε. 
a 
double The lower bound a of the interval containing a minimum. 
b 
double The upper bound b of the interval containing a minimum. 
maxcal 
integer The maximum number of calls of F(x) to be allowed. 
R interface to the NAG Fortran routine E04ABF.
E1 
double If you set e1 to 0.0 (or to any value less than ε), e1will be reset to the default value sqrt(ε) before starting the minimization process. 
E2 
double If you set e2 to 0.0 (or to any value less than ε), e2 will be reset to the default value sqrt(ε). 
A 
double An improved lower bound on the position of the minimum. 
B 
double An improved upper bound on the position of the minimum. 
MAXCAL 
integer The total number of times that funct was actually called. 
X 
double The estimated position of the minimum. 
F 
double The function value at the final point given in x. 
IFAIL 
integer ifail =0unless the function detects an error or a warning has been flagged (see the Errors section in Fortran library documentation). 
NAG
http://www.nag.co.uk/numeric/FL/nagdoc_fl23/pdf/E04/e04abf.pdf
ifail < 0 funct = function(xc) { fc < sin(xc)/xc list(FC = fc) } e1 < 0 e2 < 0 a < 3.5 b < 5 maxcal < 30 e04ab(funct, e1, e2, a, b, maxcal)