Trouble with -inf to +inf value of baroclinicity

Hello,

Can anybody please help me to solve why I am getting -inf to +inf value of
sigma. where,
sigma = (0.31*10^(-4)*dudz)*(((9.81/pt)*dtdz)^0.5)^(-1)
printVarSummary of each of the factors used in the formula are as follows:

Variable: pt
Type: float
Total Size: 422576128 bytes
            105644032 values
Number of Dimensions: 4
Dimensions and sizes: [time | 124] x [lev | 26] x [lat | 128] x [lon | 256]
Coordinates:
            time: [30.25.. 61]
            lev: [3.54463800000001..992.5560999999998]
            lat: [-88.92773535229591..88.92773535229591]
            lon: [ 0..358.59375]
Number Of Attributes: 2
  units : K
  long_name : Potential Temperature
(0)
(0) Potential Temperature: min=225.71 max=1335.75

Variable: dtdz
Type: float
Total Size: 422576128 bytes
            105644032 values
Number of Dimensions: 4
Dimensions and sizes: [time | 124] x [lev | 26] x [lat | 128] x [lon | 256]
Coordinates:
            time: [30.25.. 61]
            lev: [3.54463800000001..992.5560999999998]
            lat: [-88.92773535229591..88.92773535229591]
            lon: [ 0..358.59375]
Number Of Attributes: 2
  units : K/m
  long_name : Vertical Gradient Temperature with height
(0)
(0) Vertical Gradient Temperature with height: min=-0.00607291 max=0.126276
(0)
(0) Vertical Gradient U: min=-0.129377 max=0.142818

Variable: dudz
Type: float
Total Size: 422576128 bytes
            105644032 values
Number of Dimensions: 4
Dimensions and sizes: [time | 124] x [lev | 26] x [lat | 128] x [lon | 256]
Coordinates:
            time: [30.25.. 61]
            lev: [3.54463800000001..992.5560999999998]
            lat: [-88.92773535229591..88.92773535229591]
            lon: [ 0..358.59375]
Number Of Attributes: 2
  units : m/s/m
  long_name : Vertical Gradient U with height
(0) Vertical Gradient U with height: min=-0.0589294 max=0.0540201

Variable: sigma
Type: float
Total Size: 422576128 bytes
            105644032 values
Number of Dimensions: 4
Dimensions and sizes: [time | 124] x [lev | 26] x [lat | 128] x [lon | 256]
Coordinates:
            time: [30.25.. 61]
            lev: [3.54463800000001..992.5560999999998]
            lat: [-88.92773535229591..88.92773535229591]
            lon: [ 0..358.59375]
(0)
(0) min=-inf max=inf

Thanks,

-- 
*************************************
Soumik Basu
Graduate Student, Research Assistant
International Arctic Research Center
University of Alaska Fairbanks
Fairbanks,Alaska,USA
**************************************
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