How do you implement glOrtho for opengles 2.0? With or without tx,ty,tz values from the glOrtho spec?

Question

Im trying to implement my own glOtho function from the opengles docs http://www.khronos.org/opengles/documentation/opengles1_0/html/glOrtho.html
to modify a Projection matrix in my vertex shader. It's currently not working properly as I see my simple triangles vertices out of place. Can you please check the code below and see if i'm doing things wrong.

I've tried setting tx,ty and tz to 0 and that seems to make it render properly. Any ideas why would this be so?

void ES2Renderer::_applyOrtho(float left, float right,float bottom, float top,float near, float far) const{ 

        float a = 2.0f / (right - left);
        float b = 2.0f / (top - bottom);
        float c = -2.0f / (far - near);

        float tx = - (right + left)/(right - left);
        float ty = - (top + bottom)/(top - bottom);
        float tz = - (far + near)/(far - near);

        float ortho[16] = {
            a, 0, 0, tx,
            0, b, 0, ty,
            0, 0, c, tz,
            0, 0, 0, 1
        };


        GLint projectionUniform = glGetUniformLocation(_shaderProgram, "Projection");
        glUniformMatrix4fv(projectionUniform, 1, 0, &ortho[0]);

}

void ES2Renderer::_renderScene()const{
    GLfloat vVertices[] = {
        0.0f,  5.0f, 0.0f,  
        -5.0f, -5.0f, 0.0f,
        5.0f, -5.0f,  0.0f};

    GLuint positionAttribute = glGetAttribLocation(_shaderProgram, "Position");

    glEnableVertexAttribArray(positionAttribute);


    glVertexAttribPointer(positionAttribute, 3, GL_FLOAT, GL_FALSE, 0, vVertices);  
    glDrawArrays(GL_TRIANGLES, 0, 3);       


    glDisableVertexAttribArray(positionAttribute);

}

Vert shader

attribute vec4 Position;
uniform mat4 Projection;
void main(void){
    gl_Position = Projection*Position;
}

Solution From Nicols answer below I modifed my matrix as so and it seemed render properly

float ortho[16] = {
    a, 0, 0, 0,
    0, b, 0, 0,
    0, 0, c, 0,
    tx, ty, tz, 1
};

Important note You cannot use GL_TRUE for transpose argument for glUniform as below. opengles does not support it. it must be GL_FALSE

glUniformMatrix4fv(projectionUniform, 1, GL_TRUE, &ortho[0]);

From http://www.khronos.org/opengles/sdk/docs/man/xhtml/glUniform.xml

transpose Specifies whether to transpose the matrix as the values are loaded into the uniform variable. Must be GL_FALSE.

Answer 1

Matrices in OpenGL are column major. Unless you pass GL_TRUE as the third parameter to glUniformMatrix4fv, the matrix will effectively be transposed relative to what you would intend.