（1）固有的'log10'的'x'参数必须为实数

Question

在Fortran中通过log10函数运行迭代函数时遇到问题。

program start
integer t, dt, range, rangestart
real*8 k1, k2, k, lognmdott, nmdott, interval

dt = 10
t = 0
range = 0
rangestart = 0
interval = 0

open(unit=1, file='accretion.txt', status='unknown')

do i = 1, 200000

 t=t+dt
 range = t-rangestart

 if (range .gt. 100 .and. range .le. 300) then
  k1 = log10(1.) - log10(0.001)
  k2 = log10(200.)

  k = k1/k2

  interval = interval + dt

  lognmdott = -k*(log10(interval))

  if (interval .eq. 200) then
   interval = 0
  endif

  nmdott = 10**lognmdott

  write(1,*) t, nmdott
 endif

close(1)
end

我希望得到log10(interval)输出，其值介于10到200之间，步长为10。我实际上得到了错误

'x' argument of 'log10' intrinsic at (1) must be REAL