Matlab 提高精度 vpa

Matlab本身提供了丰富的数据类型（搜索matlab数据类型能找到详细的介绍），默认的数据类型是double型。

但是偶尔也会出现数据类型精度不够的情况，比如：计算斜率、倒数时经常出现“差之毫厘谬以千里”的现象。

因此需要提高现有数据类型的精度，matlab提供了可以自定义数据精度的函数vpa——详见Product Help或help。

需要说明的是：当不再需要高精度时，需要double(数据) -> double类型，或者其他你需要的类型。

>> help vpa
 VPA    Variable precision arithmetic.
    R = VPA(S) numerically evaluates each element of the double matrix
    S using variable precision floating point arithmetic with D decimal
    digit accuracy, where D is the current setting of DIGITS.
    The resulting R is a SYM.
 
    VPA(S,D) uses D digits, instead of the current setting of DIGITS.
    D is an integer or the SYM representation of a number.
 
    It is important to avoid the evaluation of an expression using double
    precision floating point arithmetic before it is passed to VPA.
    For example,
       phi = vpa((1+sqrt(5))/2)
    first computes a 16-digit approximation to the golden ratio, then
    converts that approximation to one with d digits, where d is the current
    setting of DIGITS.  To get full precision, use unevaluated string or
    symbolic arguments,
       phi = vpa('(1+sqrt(5))/2')
    or
       s = sym('sqrt(5)')
       phi = vpa((1+s)/2);
 
    Additional examples:
       vpa(pi,780) shows six consecutive 9's near digit 770 in the
          decimal expansion of pi.
 
       vpa(hilb(2),5) returns
 
          [    1., .50000]
          [.50000, .33333]
 
    See also double, digits.

    Overloaded methods:
       sym/vpa

    Reference page in Help browser
       doc vpa