# 多维网格
以下代码调用kernel函数, 对于多维Grid中每个线程在***全局***中的索引(x, y)正确的是?
```C++
dim3 gridDim = (blocksPerGrid, blocksPerGrid);
dim3 blockDim = (threadsPerBlock, threadsPerBlock);
....
kernel<<<gridDim, blockDim>>>(a,b,c)
....

```

## 答案

```C++
x = threadIdx.x + blockIdx.x * blockDim.x;
y = threadIdx.y + blockIdx.y * blockDim.y;
```

## 选项

### A

```C++
x = threadIdx.x + blockIdx.x ;
y = threadIdx.y + blockIdx.y ;
```

### B

```C++
x = threadIdx.x * blockDim.x ;
y = threadIdx.y * blockDim.y ;
```

### C

```C++
x = threadIdx.x ;
y = threadIdx.y ;
```