matlab中怎么保留有效位数？

[love_yjh]

比如，a=12.3648；如果我想取前三位，怎么得到a=12.3？求大神解答

[love_yjh]

输入的是double型数据，想要输出也是double型数据。

[赵4老师]

变成字符串，再变回数？

[灌水号]

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]