can't compile texture program for linear interpolation

Accelerated Computing CUDA CUDA Setup and Installation
1

I got following output when compiling,

error: no instance of overloaded function “tex2D” matches the argument list
argument types are: (texture<float, 2, cudaReadModeNormalizedFloat>, float, float)
1 error detected in the compilation of “/tmp/tmpxft_00007a9d_00000000-4_TEXF.cpp1.ii”.

//Program is,

texture<float,2,cudaReadModeNormalizedFloat> tex;

float out;
float x;
float y;
out += tex2D(tex, x ,y);

//Channel descriptor:
cudaChannelFormatDesc channelDesc = cudaCreateChannelDesc(16, 0, 0, 0, cudaChannelFormatKindSigned);