calc_expval()

template<typename Lattice , typename State >

std::string syten::calc_expval	(	Lattice const &	lat,
		State &&	a,
		State &&	b,
		SDef const &	norm,
		std::string const &	op_expr,
		int const	variance,
		bool const	column,
		bool const	realOnly,
		bool const	imagOnly,
		Index const	prec
	)

Calculates an expectation value and possibly a variance for given states, lattices and operators.

Returns a string expression for the result without newline termination.

Template Parameters

Lattice	Lattice type
State	State type

Parameters

lat	lattice on which the operator is defined
a	first state (complex-conjugated)
b	second state (not complex-conjugated)
norm	Overlap of a and b or norm of a, result will be divided by this
op_expr	operator expression, parsed with respect to lat
variance	0: no variance calculation, 1: extended output (expectation value and variance), 2: only variance
column	if true, prints real and imaginary part separated by some whitespace (overwrites realOnly and columnOnly)
realOnly	if true, only prints real part
imagOnly	if true, only prints imaginary part
prec	output precision

Returns

a string with the result, suitable for directly printing to std::cout or in a file, without trailing newline.

References abs(), syten::IPEPS::expectation(), norm(), syten::MPS::parse(), print_result(), and syten::MPS::variance().

Referenced by do_expval().

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